Help!

We need help. Friday morning our computer was infected somehow with a vicious trojan virus called AntiVirusXP 2009. It shows up as a new icon on the toolbar, a red circle with a white X. It constantly flashes a badly spelled warning in broken English advising that our system has been compromised and trying to get us to download a bogus virus killer.

Worse, it has completely disabled all the virus protection we had, so our computer is now naked to the world. So we are only using it very sparingly, and unplugging the modem the rest of the time.

We are running Windows 2000 Professional, and need recommendations for reliable virus killing programs we can download and run that will get rid of this thing. Because it is trying to get us to buy a bogus virus killer, we are being very wary of downloading any other virus killer without recommendations. If anyone out there can help with this, we would really appreciate it.

We can't install any new firewalls or other protections until we get this Trojan off our system. We've tried Ad-Aware, but it doesn't seem to touch it.

Thanks in advance for anything anyone can do or suggest.

UPDATE 11/9/08 8:21 am

Okay. After a hellish weekend trying to deal with this trojan, I've finally beaten the goddam thing. I could detail the wasted Friday evening Nate and I spent trying to figure out how to get rid of the thing ourselves, then the wasted late Friday night I spent buying new security software from Symantech, which I thought would kill the virus, but which, it turns out, will only prevent new viruses in the future, and will not load propertly while there is a virus in the system, and then the wasted Friday night/early Saturday morning I spent trying to install the new security software from Symantech, then the wasted Saturday morning I spent on the phone with Symantech for about three hours (after their tech support chat software mysteriously stopped working on our computer) trying to get them to either (a) disinfect our computer for free (they wanted $100 to have some tech do it by remote control from the Phillipines; as I had already paid $65 for software that would not load, I was not going for that crap) or (b) refund my money for the software that would not load, then the waste of Saturday evening, night, and much of Sunday morning running four or five different free virus scan/destroy programs that took hours to run, and then, when they were done, couldn't get rid of the Trojan.

I could detail all of that, but finally, around 4 am, I ran across Malwarebytes' Anti-Malware, and it scanned in ten minutes and then deleted the virus entirely, and now the virus is gone and my new Symantec security software has installed and all is well.

All is well.

With the computer, anyway. SuperWife has some kind of respiratory thing in her chest and she's taking some serious meds for it, and Super Adorable Kid won't stop coughing, and I'm getting a scratchy throat and my head is stuffed up. But at least I fixed the frickin' computer.