First, remember to back up all the important files like burn it to a CD or DVD...
Then, when you first boot up the computer, press DEL key to go into Setup. Then, highlight something that called "BIOS" like BIOS Setup or the sort and press enter.
Then go to First Boot Device and select CD-ROM.
Then go to Second Boot Device and select HDD-0.
Exit and save.
Insert the disc Windows XP into the computer and restart. When it ask if you want to boot up from disc, press any key to enter so it will boot up Windows XP. When it boot up windows xp and ask you if you want to Format everything from your HDD, choose that option and choose "install a fresh copy of Windows XP". I can\'t remember the exact order in there, but that\'s what you should select though so the disc will format everything in your HDD meaning all files will be deleted.
After it finish formatting, it will install a Fresh Copy of Windows XP. Then there will be times during installation, it will restart computer and remember not to press enter again when it ask you if you want to boot up from disc. As it will automatically finish where it start off installing windows XP. During installation, they will ask you some questions like username, etc. After it finish installation and stuff, you should see Windows being boot up and the background which means you have successfully install it...
And here is a picture of BIOS so you can get a better idea of what i mean when choose CD-ROM as your first bootup device...
