Using system restore can correct damage done by a virus, but if you really do have a virus, it will redo the damage anyway. As Jana said, it's best just to wipe the hard drive out and start all over, unless you have someone that can effectively get rid of them. If restore points have been set since you were infected, then the virus could very well be stored in your system restore now as well. And as Mike said, use Avast. It will let you schedule a "boot-time scan", which is a much better way to clean viruses, because it loads and scans before Windows loads. One of the biggest problems in getting rid of a virus, is that a file cannot be deleted or moved when it's in use, so that's the biggest benefit of having a "boot-time scan". And I'm not up on things as much as I used to be, but I don't know of another antivirus that will do that.
Download Avast Here
Other helpful spyware, adware & malware removal tools are
Spybot Search & Destroy and
Adaware
If you choose to install any of these, make sure they are updated with the latest removal definitions before doing the scans. These scans can take a long time, depending on how much software is on your computer, and how infected it is, so be ready for that.