How do you increase the CPU Usage on my XP?

Try running CPU Burn-in; it stress-tests your processor.

http://users.bigpond.net.au/cpuburn/

When was your most recent system check-up/maintenance?

eg.
Disk and Registry Defrag,
Malware Scan,
Desk Clean-up, etc.

Posting specs of your comp and explaining what task(s)/program(s) are running slow would help you get more informative answers.

i dont know why you would want to increase your usage lol but i imagine your talking about speed and in that case you could overclock (oc) it by using an oc utility or your bios but i dont feel to comfortable doing this because it has a chance of frying your processor if you push it to far but if you are interested you can ask how to overclock and get help from someone with more experience in that field or look up guides online

I dont understand why you would want to increase the cpu usage? Install nero 7 my cpu idled at around 50% usage ha

If you want to make you computer run faster delete old programs you know longer use. You can find good programs free on the net to clean up your computer like temp files an you registry but i dont know any