Vista - Automatic update - video conflict

I run Vista Ultimate on a IMAC (26" Dual core 2.8ghz) which works generally
very well. Two points I have observed.
1. It seemed that the screen it would randomly reduce in resolution and
then often start to flash uncontrollably. It seems that this occurs only
after an automatic update has finished downloading. I had my suspicions and
then I witnessed it first hand. One for the testers!
2. I have also observed that if you attempt to start Explorer before Vista
has properly started then Explorer will crash. Starts again fine but clearly
a glitch.
That's all!