Speed is speed dude. Under the conditions stated above, a format can make a marvelous difference. I just formatted and noticed a drastic performance increase in all emus, games, and winxp itself.
1)
Hell why format ? Just kill Program Files and all windows subdirs except COMMAND in DOS mode.
Then install windows again. No need to move your music, DOS games etc.
2) If your system works ok (no BSOD) but loads slow. Why don't use registry cleaning proggie ?