This is a 160 page XP tweak guide.
The guy who wrote it also has tweak guides for Nvidia cards, Far Cry, and HL2, and much more.
Using this guide I have tinkered with virtual memory, disabled many programs I don't need, removed many programs from start menu, and cleaned off some wasted space on my hard drive.
This has my PC running a little faster, games a little faster, and startup time is a lot faster.
It's a good free guide if you have some time on your hands & want to maximize your PC.