I have personally used the above link before and had much success in ridding my desktop of trojans and viruses that AVG just would not touch.
These people are great! It is a free site and you have to be patient if you decide to listen to them and let them help you get rid of the junk. They give great instructions and walk you through exactly what you need to do to get rid of the really stubborn stuff. They help so many people so somtimes it takes them a day or a few hours to get back to you. I did a lot of reading at the site on my own that helped me even further.
I give them kudos for cleaning my machine! I have kept HijackThis and MalwareBytes Anti-Malware (free software that they ask you to download to help and they tell you how to use) on my machine since and run them ever so often to make sure my machine stays clean. You need to know what you are doing though to run those programs, so I am not suggesting that anyone use them without the help from those tech guys.