Despite all nice ideas in here I just want to bring something up that could
cause this behaviour.
RAM.
If your memory is full, Windows will start paging inactive areas of the RAM
onto the harddrive to free up some space in the ram modules, thus creating a
lot of harddrive activity. I know that Vista got 8 times more (yes 8 times!)
RAM requirement than it's predecessor Windows XP (min. 64mb), but 512 mb
should still be enough to run Vista smoothly and without paging from what
I've heard...
Well, just wanted to bring it up, you never know

.
--
/Robert