Explorer.exe CPU Usage

When I do certain tasks like "show desktop", use Windows Media player 11, or
open up IE7 my computer will hang for 10-20seconds and will show Explorer.exe
using as much of my CPU as possible, ensuring my total CPU usage is at 100%.

It does this quite frequently, I was wondering if anybody had a similar
experience and found a solution, or if there are any suggestions.

My System is as follows

Vista Beta 2
AMD 3700+
Nvidia 7800 GT
2 Gigs of Ram
300GB Harddrive

Thank you.