[fishscale]

I've seen a variant that puts a password on your hard drive. Not a BIOS password, a hard drive password, so if you take the hard drive and try to access it from another computer, you won't be able to. Be careful with this one.

Hijack This is always the old standby, but it's got a bit of a learning curve.
Personally, I'd make a live CD and scan from there. Check for rootkits while you're at it. (You might get false positives, or you might not find malicious rootkits either. I try not to think too much about security anymore.)