Originally Posted by shakran

Some of the commercial antivirus programs, such as Norton, come with a CD that you can use as an emergency recovery CD. You boot off the CD, it does a virus scan without running windows, and therefore without triggering the virii to stop everything from working.

Also, try installing a skeletal OS + AVG/spybot on a portable hard drive and booting off of that drive, then run the scans on your system drive from it.