The best 'tweaking processes' guide to be found on the 'net, I believe, is on BackViper's website:
http://www.blackviper.com/WinXP/servicecfg.htm
http://www.blackviper.com/WIN2K/servicecfg.htm
If you make the changes for his suggestion of a 'Safe' configuration, you'll end up with a leaner, meaner Windows install. But give it a good read through first, and use Google to track down more info about bits 'n' pieces you don't follow. If you disable a service that's required for some computing task you actually want to USE, then you can always re-enable it afterwards :D
Doing your 'homework' in preparation is essential before you go diving in!
Have fun :D