I had similar problems with Vista 64. What I did was disable a few services:

- Superfetch
- Defrag
- Search Indexer

Now, I don't need any of these services, so it didn't impact me in any way. It may impact you (if you do a lot of searching on your hard drive, for example), so you may have to make a trade off.

Here's a resource I use when I want to figure out what a service does, and to help me decide whether I can turn it off or not:

http://www.blackviper.com/

Hope this helps!