For anyone who has stumbled upon this thread in desperation. XP Antivirus is the Virtumonde Virus by any other name, download "Vundofix" or "VirtumundoBeGone" tool. DO NOT pay for any removal tool for this threat, the threat is well documented and easy enough to remove yourself for free. i am amazed that customers are still paying a friend of mine £40 to remove this nuisance.
Spybot S&D is still being updated frequently, a machine I use it on has taken three updates in the last fifteen days to 12/11/08. I note a selling angle?