This could be due to the manner in which our particular SBS 2000 server is
configured, or 3rd party applications running on it (Trend, GFI, and ISS
products), but in case not, it seems worth reporting:

After installing the latest round of MS critical updates yesterday (834707,
8 33989, 841356, 840987, 841533, 824151) our server would not reboot, except
in safe mode. Uninstalling the critical updates didn't solve the problem,
nor did restoration of system state, nor did five hours on the phone with MS
tech support, during which we removed all 3rd party apps.

Problem was only cured by complete restoration of the OS drive from backup.