If it's added the entry to the startup folder, then that's a problem. It will never be deleted. There are a number of startup folders depending on the users, but likely they chose a generic one:
The easiest way to find it is to: click START, run, msconfig
C:\Documents and Settings\All Users\Start Menu\Programs\Startup
Then select the Startup tab and look for the Startup Item named wubi. It will show the location of the program as well as where it was added. It should be the RunOnce part of the registry.