A couple of tips I got from a computer magazine recently which seem to have worked with my laptop running Win XP SP2

Go to "My Computer",. right click on the Hard drive icon and select "Properties"

In the "General" Tab, uncheck the box labelled "Allow indexing service the index this disk for fast file searching".

The File indexing service takes over periodically and you cannot use the computer at all while it is chattering away. Unless you use the search facility, frequently, it is not needed.

Also on this tab, is a button labelled "Disk Cleanup". Checking this will cause the computer to get rid of temporary files and other fragments that clutter the hard drive. I did this and recovered between 3 & 4 meg of hard drive. It takes several hours, so set aside time to do this.

I also ran msconfig and unchecked a lot of the files that start up during booting and then run in the background

Since doing this, I have found that my computer boots more quickly and I get fewer problems with the computer taking over and chattering away to no apparent effect. It still happens, but less frequently.