How to remove something from Add/Remove Programs

This is documented in Microsoft kb 314481 here:
http://support.microsoft.com/kb/314481
but in case it ever moves....

The Currently installed programs list in the Add or Remove Programs tool lists all of the Windows-compatible programs that have an uninstall program or feature. Occasionally, a program may not be removed completely, and the registry key that is used to display the program in the Currently installed programs list remains. In this situation, you may need to manually remove the program from the Currently installed programs list in Add or Remove Programs.

Remove the program's entry from here:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall