Hi,
I guess that you mean that the app is physically removed, but an uninstall entry still exists in the add/remove programs applet...
The entroes listed here are stored in the registry in the following key...
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\
If you have successfully uninstalled the app, and just want to get rid of the entry in the applet, simply remove the offending subkey from this key...
Regards
John