|Obviously you will need an XP disc & since your sysytem apparently shipped with Win7, it most likely has a SATA HDD. That means you will need to load the SATA/RAID drivers at the start of the XP installation or the HDD will not be recognized. An alternate method would be to change the SATA setting in the BIOS or slipstream the SATA/RAID drivers into the XP disc. If you know what you're doing, it's fairly simple, if you're a newb, it's not going to be easy.|
And as stated by StuartS, you will need to find all the necessary XP device drivers (chipset, video, audio, network, wireless, etc). Remember that XP is about 10 yrs old now. I'm sure your system uses modern hardware devices therefore the XP disc will not have many of the required drivers. And there's a chance that the hardware manufacturer didn't even bother to develop drivers for XP. Make sure you do all the prep work before you wipe the drive.