From itsamac.com
(please note - this is a copy of info found on the above site. I'm mirroring it because I think it's useful. Credit for this article is due entirely to Itsamac)

How to Install Zen Cart eCommerce System

"What you would use this for: To offer an online catalog and shopping cart for your visitors to view a description of products and make purchases.

What You Need:
An FTP client (Transmit - external link)
A MySQL Database (if you don't already have one setup for your site, please request one)

1. Go to http://www.zencart.com (external link) and download the latest ZenCart installation by clicking the "Download Zen Cart Now!" graphic. We'll refer to this as the zencart.zip file.

2. If the installation package doesn't expand automatically, double click the zencart.zip file. This should force the compressed files in zencart.zip to expand into a folder that begins with "zen-cart", followed by a version number. We'll refer to this folder the zencart folder from now on.

3. Upload the contents of the zencart folder into your public_html folder on the server. Alternatively you could create a folder inside your public_html to upload into (i.e. public_html/zencart).

4. Change the file permissions on the following folders on the server to 777:

/cache/
/images/ (including all subdirectories), /includes/languages/english/html_includes/ (including all subdirectories)
/media/
/pub/
/admin/backups
and /admin/images/graphs/

To change file permissions using Transmit, highlight each folder individually and press command + i. In the window that pops up, you can either type 777 into the bottom field or make sure all boxes are checked.

5. Rename /admin/includes/dist-configure.php to configure.php. After renaming it, set the file permissions to 777.

6. Point your web browser to http://www.yourwebsite.com/zc_install/ (If you installed ZenCart into a sub-folder it would be http://www.yourwebsite.com/zencartfolder/zc_install/)

7. Click "Continue" at the welcome screen, on the next page, read through the GNU license then click "I have read and agree to abide by the Terms and Conditions as stated above." Click "Continue".

8. The next page is the system inspection page. There may be a few yellow explination point icons next some items. Don't worry about these. If you have any red "X"'s next to any items, these need to be fixed. Refer back to steps 4 and 5. Once everything checks out ok, click the "Install" button at the bottom of the page.

9. The next page is the system settings page. Look below for example settings. The # sign after the secure portion of the web address depends on what server your site is on. If you need SSL setup on your site, or are unsure what SSL server you are on, please contact us.

Physical Path: /Library/WebServer/WebSites/YourUsername/public_html/ (replace YourUsername with your itsamac ftp username) (if you installed ZenCart to a subdirectory remember to include that after /public_html/)
Virtual HTTP Path: http://www.yoursite.com (if you installed ZenCart to a subdirectory remember to include it!)
Virtual HTTPS Server: https://secure#.itsamac.com/www.yoursite.com (if you installed ZenCart to a subdirectory remember to include it!)
Virtual HTTPS Path: https://secure.itsamac.com/www.examplesite.com (if you installed ZenCart to a subdirectory remember to include it!)

Check both "Enable SSL", and "Enable SSL in Admin Area" if you already have SSL setup. Next, click the "Save System Settings" button at the bottom of the page.

10. Select "No" next to the "Do you want to use phpBB forums" question, then click the "Save phpBB Settings" button. (If you'd like to use phpBB with your ZenCart system you can set that up later. We offer step by step instruction in our how to's support section.)

11. The next page is the Database Setup page. Look below for example settings for this page.

Database Type: "MySQL"
Store Identifier (Table-Prefix): "Leave this section blank"
Database Host: your mysql server (Replace "your mysql server" with the location of your MySql database as indicated in the e-mail "From Itsamac: Your MySQL access is set up".)
Database Username: your MySql username (usually your itsamac ftp username)
Database Password: your MySql password
Database Name: yourMySQLusername_db (usually your itsamac ftp username followed by _db)
Database Sessions: Yes (this is the default setting, you can change it to no if you'd like)
SQL Cache Method: None (this is the default setting, you can change it if you'd like)
Session/SQL Cache Directory: /Library/WebServer/WebSites/YourUsername/public_html/cache (replace YourUsername with your itsamac ftp username) (if you installed ZenCart to a subdirectory remember to include that after /public_html/)

Next, click the "Save Database Settings" button at the bottom of the page.

12. The next page is your Store Setup page. Fill in the blanks and click the "Save Store Settings" button at the bottom of the page.

13. The next page is used to setup an administrator account. Use the following settings:

Administrator's Username: YourUsername (or any username you would like to use)
Administrator's Password: YourPassword (or any password you would like to use)
Administrator's Email: your e-mail address

Click the "Save Admin Settings" button at the bottom of the page.

14. Congratulations! You have successfully installed Zen Cart™ on your system!

15. Delete the install folder from your webspace. /public_html/zc_install

16. Set the file permission for /includes/configure.php and /admin/includes/configure.php to 644.

17. You're done! You can now start using your ZenCart system!"

and

How to Install OsCommerce

"What you would use this for: To offer an online catalog and shopping cart for your visitors to view a description of products and make purchases.

What You Need:
An FTP client (Transmit - external link)
A text editor (TextWrangler - external link)
A MySQL Database (if you don't already have one setup for your site, please request one)

1. Go to http://www.oscommerce.com/ (external link) and download the latest Linux/Unix osCommerce installation package from the downloads section. We'll refer to this as the oscommerce.tar file. It is also a good idea to download the PDF documentation for osCommerce as well.

2. If the installation package doesn't expand automatically, double click
the oscommerce.tar file. This should force the compressed oscommerce.tar to expand into a folder that begins with "oscommerce", followed by a version number. We'll refer to this folder the oscommerce folder from now on.

3. Navigate into your oscommerce folder and find a folder called "catalog".

4. Upload the catalog folder into your "public_html" on the server.

5. Change the file permissions on the following file on the server to 777.
/catalog/includes/configure.php and /catalog/admin/includes/configure.php To do this using Transmit, highlight each folder individually and press command + i. In the window that pops up, you can either type 777 into the bottom field or make sure all boxes are checked.

6. Once all the files are successfully uploaded point your browser to: http://www.yourdomain.com/catalog/install/ - click "Install new online store". On the next screen make sure both check boxes on the next screen are checked and click "Continue"

7. Enter the following settings:
Database Server: your MySql server (Replace with the location of your MySql database as indicated in the e-mail "From Itsamac: Your MySQL access is set up".)
Username: your MySql username (usually your Itsamac ftp username)
Password: your MySql password (usually your Itsamac ftp password)
Database Name: YourUsername_db (replace YourUsername with your Itsamac username)
Persistent Connections: leave unchecked
Session Storage: Check Database
Click "Continue"

8. Click "Continue" on the Database Import page.

9. Enter the following settings: (replace "examplesite.com" with your website name, and "YourUsername" with the ftp username for your site.)
WWW Address: http://www.examplesite.com/catalog
Webserver Root Directory: /Library/WebServer/WebSites/YourUsername/public_html/catalog
HTTP Cookie Domain: www.examplesite.com
HTTP Cookie Path: /catalog/
Enable SSL Connections: If you have SSL enabled for your website check this box (contact us for questions regarding SSL)
Click "Continue"

10. Verify the osCommerce Configuration information is correct. This is the same information that you entered earlier. Click "Continue" - This should bring up a page that says "The configuration was successful!"

11. Delete the install folder from your webspace. /public_html/catalog/install/

12. Change the file permissions on the following files and folders:
/catalog/includes/configure.php to 644
/catalog/images to 777
/catalog/admin/includes/configure.php to 644
/catalog/admin/images/graphs/ to 777

13. Create a new folder called backups and upload it in the public_html/catalog/admin/ directory (in Transmit make sure you are in the directory and click the "New Folder" icon at the top)

14. The last task is to password protect your admin directory (public_html/catalog/admin/)
You can do this through any PHP or CGI script that creates a .htaccess file. We recommend using this automated .htaccess generator: http://www.webmaster-toolkit.com/htaccess-generator.shtml (external link)

15. Use the following settings:
Username: YourUsername (or any username you would like to use)
Password: YourPassword (or any password you would like to use)
Path: /Library/WebServer/WebSites/YourUsername/public_html/catalog/admin (replace "YourUsername" with the ftp username for your site)
Click the "Generate .htaccess" button

16. On the resulting page copy the text from the first box (hightlight the text and press command + C). Next, open TextWrangler and press command + V to paste this text in TextWrangler. Save this file as "htaccess" (without the quotes) by going under File/Save As in the menu. Do the same thing for the next text box and save this file as "htpasswd" (without the quotes).

17. Once the files are created upload them into your admin directory.

18. We now have to change the file names to include a period in front of htaccess and htpasswd. Adding the period in front will make the files readable by the server and invisible via your FTP browser (so don't panic if you can't see those files after you make this change). In transmit hightlight htaccess and click File > Rename in the menu. Rename this file ".htaccess" (without the quotes) and press return. Hightlight htpasswd, rename this file ".htpasswd" (without the quotes) and press return. Your admin folder is now password protected, and you are ready to begin using osCommerce."