if you have particulary nasty spyware, then the best choice is HijackThis
the problem is that the program is totally manual. You need to know what is good and what is bad in the log file it creates. One of the best places to go to get help with this is:
http://forums.thatcomputerguy.us/
They have really good help and advice on clearing spyware. You can get HijackThis from their downloads link at the top of the page. Run the program, then post the log file in their spyware forum.
The box said 'Requires Windows XP or better'. So I installed Linux.