I read a few hundred more pages on this and no one really knows for sure what is causing it yet. A few theories, but nothing conclusive.
1. One person updated their ATI video drivers
and it stopped.
2. Another turned off Indexing services and it stopped.
3. Did you do a upgrade install for Vista from within XP instead of doing a clean install with the upgrade?
I noticed that this has been the cause of a lot of mysterious problems.
You might try updating your video drivers, it wouldn't hurt anything.
If it is just driving you nuts, you could disable the Superfetch service until there is a known solution for the problem found. Just follow the same steps in the earlier post, but do STOP and then DISABLE.
I'm out of ideas until something else pops up on it.
Hope this helps some,