Open the folder Program Files\Adobe\Acrobat 6 (or whatever)\Reader\Plug_ins.

Move all files except EWH32.api, search.api and printme.api into the 'Optionals' folder.

Open Acrobat Reader. Edit > Preferences > Startup. Uncheck 'Display Splash Screen'.

Update 27/12/05:
More here...
http://insidemicrosoft.blogspot.com/2004/12/how-to-optimize-adobe-reader-70.html