Put in the windows xp disc and run the install. If you don't have one, you have to buy it from somewhere. Why don't you just go to windows 7? Windows xp is not supported by microsoft anymore and they won't release any major updates for it.
you want to use a hirem boot cd. boot from the cd and do an fdisk and remove all the partion on the hard drive and then do an fdisk/mbr to remove window 8 boot loader from the mbr. put in your windows xp oem or retail cd and set your bios to boot from the cd. before you start make a cd or a usb stick and have on it the intel chipset drivers for the mb..and network drivers and the sound drivers. when windows xp starts have the usb stick or cd ready. hit f6 to do a custom install of the drivers and let xp install the inf for the chipset/usb/sound/ethernet. before you wipe windows 8 if your system was a pre built check to see if it run windows 7/xp some pre builts wont do to bios bugs.