I uninstalled Prism Version 3.03 and I am still getting a listing for Graphpad Prism 3.03 in the "Add/Remove.." window of the Control Panel. .

You found a real glitch. The Prism 3.03 updater put an invalid entry into the registry to "run" an uninstaller that doesn't actually exist (as you've discovered). You can just leave the entry there. It doesn't do any harm. You'll just see an extra entry in the add/remove programs list. But if that extra entry bothers you, you can remove it:

1. Click Start and select Run.
2. Enter "regedit", click OK.
3. Using the registry Editor, find: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall\{BE65B7 C0-89ED-11D6-B2FA-000102AF9672} 
4. Right click on that entry and delete it.

Editing the registry is a big deal. Do so slowly and carefully at a time when you won't be distracted. You really don't want to accidentally delete the wrong entry (some entries are crucial).