Just for extra assurance, I'd recommend downloading, burning and running a bootable CD with it's own stand-alone anti-virus checker.
Here's 2 examples:
http://www.majorgeeks.com/Avira_AntiVir_Rescue_System_d6005.html
http://www.majorgeeks.com/Kaspersky_Rescue_Disk_d6501.html
Combofix is similar in function, but doesn't require burning a CD
http://www.majorgeeks.com/Combofix_d6402.html
Thanks Vailr,
Can these be run from a flash drive as well?