|You need professional help!|
To install xp you need a proper xp install disk for the version you have (most commonly XP Home OEM) and the xp key from the COA which should be stuck to your machine. You boot the machine from the CD, then follow the instructions. When you get to the screen where it asks where you want to install XP, if your disk has a dead xp on it you are best formatting the drive when offered that option to clean all the old stuff off (unless you have documents/pictures etc on there you want to recover - as formatting will wipe everything). Once installed, you'll probably need to find drivers for some of the hardware (xp has its own, but rarely has some for all hardware in a machine). To do this you'll need to know what the hardware is called and visit the manufacturer's sites.
So I suspect you will need professional help.