Just read the allstarfaces thread about a virus.
The best way to start to get rid of viruses, trojans etc is to turn off Windows restore as the virus is sat hiding in the files and will come back and re-infect.
Then open windows in safe mode and run all your virus,adware and trojan checkers. The winlogon32.exe referred to in the above post is a trojan horse.
There is a bit of advice about it here although you don't necessarily have to download their software.
Here is a comparison of all the main anti virus products which may help you choose which one that you want to use.