Sasser (and it's three variants) and the latest version of GaoBot have been my life the past few days. But this outbreak is nothing compared to the biggies of the past couple of years. Nimda and SQLSlammer were the biggies, with Blaster close behind.
You can just kill the avserve2.exe process and delete the %windir%/avserve2.exe file in the 60 seconds to reboot. That will stop the worm from restering on reboot. Then you can get the tool and cleanup.
Let me just take this opportunity to make a Public Service Announcement:
Everyone, please run a firewall on your high speed connections! There are plenty of free personal firewall programs out there, if you don't have a hardware firewall. Also, please patch your systems! Microsoft has provided the automatic update client to automatically check for and install patches on 2000 and XP. Also, please get an anti-virus program and run it. If it isn't already, configure it to automatically check for updates as well. If everyone did these three things, viruses like Sasser wouldn't create half the impact they do today.
Ah, there, now I feel better.