Just a heads up, but I've seen 14 computers now that the Microsoft critical update for the Sasser worm (835732)
http://www.microsoft.com/technet/security/bulletin/ms04-011.mspx has broken. Two of them had to be reloaded from scratch. Windows 2000 and XP both seem to have problems with this patch. (Note that not every computer has a problem, it depends on what other programs/drivers are installed on the PCs.)
Generally what I've been seeing is that the system will hang at bootup. Windows 2000 systems with a VPN connection setup almost all seem to be affected. Microsoft has a patch available for Windows 2000 that you can apply before the hotfix to keep this from happening, but you have to call them to be allowed to receive it. I've now seen the exact same thing happen to an XP Pro machine, even though Microsoft has not admitted XP is affected.
Basically if the patch does not keep your system from booting (even in safe mode), you can uninstall the 835732 hotfix from the control panel and then in some cases get the hotfix for the hotfix (by calling Microsoft and waiting on the phone for an hour), install it first, then reinstall the 835732 hotfix again and pray that everything still works.
(I really wish Microsoft would test their patches before releasing them to the world and causing people like me hours of endless entertainment for the past couple weeks trying to track down which one (or more) of the 10 billion security patches for Windows is breaking my systems... It's even better when the automatic updates utility automatically allows the users to break their systems and not know what happened. I think Microsoft should have to pay my $185/hour consulting fee for the 20+ hours I've spent recently dealing with this horrible patch.)