It's possible that your problem isn't actually caused by an infection. How long has this been happening? What were you doing when it first happened? Have you tried System Restore? Last known good configuration?
It first happened after I restarted it, shortly after I installed the Sims 2, along with a keygen. I remember doing a scan, and finding a trojan, with "Sims 2 keygen" in it's name somewhere...
EVERY TIME I do AVG Anti-Spyware scans, I find "hijacker.small". I put it in quarantine, I try deleting it, but it just regenerates... I don't know if that could cause my problem, maybe..
I tried "Last Know Good Configuration" and System Restore was turned off.