Avg just released an ISO for a bootable AV disk. Burn the disk on a clean PC then put in infested PC. I haven't tried it as I just D/L'd yesterday so don't know if it'll work or not. I do know that when your rebooting the machine your reloading the virus over and over again. You'll have to get a bootable disk to avoid the windows startup. Google AVG ISO and you'll find it.
If it's rootkit protected you may have to get a Linux based ISO. I have used them with GREAT sucess. Just plug them in, hit update then scan and delete. Takes about an hour to scan.
Use Firefox 3.6 as it's more secure. Get the WOT (World of Trust) plug-in. It show a color coded circle for rated sites, Green for good, yellow for suspicious and red for harmful.
If it gets infected that often it's time to change surfing habits.
Might also look into a flltering software to keep the kids off the bad sites.