Is it one of those "lol, u have a virus, pay us money to get rid of it" viruses? Those suck balls. Basically try to find all the offending EXEs (go into Task Manager and look for anything wierd), go into safe mode and delete them. Then run Spybot Search & Destroy, HijackThis, and whatever anti-virus program you have (or download Microsoft Security Essentials and run it if you don't have one) a couple of times until everything looks clean.