1. Go with scanning your PC first using one of the Internet scanning sites (Panda as someone mentioned, Symantec) and remove anything found. You may have to follow special instructions if anything is found.
2. Run this utility (CWShredder) http://www.spywareinfo.com/~merijn/files/CWShredder.exe (make sure you update it prior to scanning). Fix/remove any problems.
3. Boot into safe mode and try anti-virus scan again

Then protect yourself, resources:
* Replace HOSTS file with file located here http://www.mvps.org/winhelp2002
* Browser Hijacking info: http://www.spywareinfo.com/articles/hijacked/
* Preventing spyware from being installed: http://www.spywareinfo.com/articles/...ed/prevent.php

Good luck.