The location of startup files has changed in version CS3.
The lirbary folder is hidden in Mac OS Lion and above, you can access it like this: http://osxdaily.com/2011/07/22/access-user-library-folder-in-os-x-lion/
Okay, so if the location has changed, where is that new location???
Follow the instructions in the link above; then go to HD/users/<yourname>Library/Application Support/Adobe/Adobe Illustrator CSX/en_US/New Document profiles.