DO NOT fiddle with your Registry if you are not a professional, you can turn your PC into toast VERY easily.
The easiest way to get his thing off you computer is: 1) Use autoruns to stop it starting at boot time. 2) reboot the PC 3) run you usual anti-virus.
I haven't tried this removal tool but it MAY work http://removal-tool.com/personal-antivirus-personalantivirus/
BTW. If it came back like that take it back and get the idiot who got it infected to remove it.
T, June 2009