Well this morning I downloaded 3 of the 4 updates Windows proposed - downloaded KB951748 (Windows XP safety), KB953465 (unwanted e-mail filter) and KB953432 (Office Outlook 2003 update) - and I've not had any problems after resetting my PC.
The only one I didn't download was the Malicious Software Removal Tool KB890830 (
http://support.microsoft.com/kb/890830), as it came up with some licence agreement I had to accept so I decided not to bother. Presumably if there is a problem with the Windows updates, it must be with that part of it.