How do you remove Trojan horse downloader wintrim AV?

The free anti virus software AVG 6 was not effective on the first try although it did detect the virus which Norton antivirus did not. After using the Windows XP system restore to go back to a date before the virus had installed itself the AVG6 still detected the virus but also allowed me to delete it by using the AVG 6 Virus Vault Delete method.