Found this important information on the Service Pack 1. Probably NOT a good idea to install it if you aren't a registry techie! Microsoft glitch offers up Vista SP1 early | Beyond Binary - A blog by Ina Fried - CNET News.com
Microsoft glitch offers up Vista SP1 early.
The glitch is the second SP1-related issue for Microsoft in recent days. The company had to pull another update, this one a set of files necessary to move to SP1, because some users were sent into a repeated reboot cycle by the files.

I purchased a program called SpyHunter, and I was prepared to do a complete system recovery because Windows Explorer loops through the close/restart cycle, and the issue was progressively getting worse. I couldn't do anything on my computer without it closing and reopening. It was getting annoying to say the least.

So my last option before system recovery was to try SpyHunter (even though I already run a new version of Norton and Registry Pro). Norton supposedly checks for VIRUSES, netbots, etc! NOT!!!! It obviously wasn't cleaning up, fixing, repairing, or deleting anything.

Ran SpyHunter, and VOILA! for 2 days Windows Explorer has not continually looped through a shut down/restart process.

This is almost to good to be true. Jury is still out on this, but so far so good.