Had the Blue Screen of Death on two of our computers recently. Both running Vista.
You might try BlueScreenView, a free program from
NirSoft - freeware utilities: password recovery, system utilities, desktop utilities This analyses the minidump made when the system crashes and points to possible causes. In my case, it pointed to Avast, which combined with a Vista update might have been the cause. Upgraded Avast to the latest version, and (touch wood) no issues since.