See http://vil.nai.com/vil/content/v_325520.htm in particular the removal tab and see the instructions there for ME/XP also apply to Vista/Windows 7 (I wish they'd update their links, we have asked many times). Basically disable System Restore and if necessary tro scanning in Safe Mode. To reach that tap F8 repeatedly while booting up and once in that mode, go to Computer (Vista/Win 7), My Computer (XP) and then right-click the hard drive and select Scan from the drop-down menu.
You'll see only taskbar activity and hovering over that will give you a progress report.
That should get rid of it.
Once you are sure it's gone re-enable System Restore.