Are there guides/tips/tweaks/recommendations to try to tweak or increase your system/cpu/hardware performance as much as possible or solely do some fine tweaking for NLE video-editing purposes on Windows XP?

knock yourself out:

http://www.videoguys.com/WinXP.html

Probably the best tweak tips ever. At the same time you learn about XP shell program. Believe me, this is one intensive and thorough procedure but worthi it. A top TEN!