If you have encountered this issue where you run Task Manager and find that an instance of svchost.exe is taking up 100% of your CPU cycles and upon killing said instance your computer runs fine, you may have an issue with Microsoft Updates. Microsoft Update is the new tool from Microsoft that lets you get updates for Office as well as Windows.
I searched around and found this site which is the SysInternals message board. I used ProcessExplorer to figure out that svchost.exe was taking up 100% of the system resources. His actually happened to me a few weeks ago but as of 5/7/07 Microsoft has released another patch that supposedly fixes this problem. It worked on the unit I was working on so that’s a good sign. I was reading through many different newsgroups and forums with mixed results.
In any case, here is the link to the KB and the actual download.