Not being a cpu-wiz(nor data-retard
I'm assuming it's the registry database.
I've tried it before, when I've deleted worms with avast, thus making it impossible to start anything (programs/.exe-files).
The first times I could manage by starting XP in commando prompt and DOS'ing my way to system restore/system recovery (c:windows/system32/restore/rstrui.exe - I believe it is).
This time, I haven't able to do that, as it wouldn't even start that.
Thanks to a file at Annoyances.org, it fixes this, apparently common, problem with anti-virus programs.
The problem is now that I have to intstall this file each time I start or reboot my computer, to get any of the files to work.
Besides that, now I can only be a limited time on the net, before I get mysterously half unhooked and can't access between none to some websites, differing from time to time (also my Kerio-firewall starts saying not connected in an error-message).
That's my problem, which started after detection of worms and subsequently deleting them or putting them to vault(what ever was possible) with Avast!.