I've been lurking quite a bit, whilst I work on my diy cnc mill. Absorbing the vast amount of knowledge here, but at last found something I might be able to contribute.
http://www.blackviper.com/
This site explains all of the services running under XP/2000 that are really not required and offers downloadable files to eliminate those unnecessary services. Read carefully, but I believe you'll find it quite worthwhile and usually a nice improvement.