hmm... P1 lol, XP can be installed on alot of computers, but i think you may be pushin it. How many mhz is that!?!
If it is able to hold it (you need 233-MHz minimum Processor, 1.5 gb hard drive space, 64mb RAM min(not reccomended), Super VGA (800 × 600) or higher resolution video adapter and monitor)
Those are the MINIMUM required specs.
If you have the XP cd, just put it in, you should get a screen that says upgrade or other features etc, (if not just put the cd in, restart and you should get a blue screen to continue setup). Choose the partition you want to install it in, since you want to reformat, you will want to format it before you install XP. It really isnt that hard, I dont have enough time to write a tutorial, but if you search the web, im sure you could find something if this doesnt help you.
GOOD LUCK!
~Evo