there are a lot of different xp pro cds out that. you oem serial should work on most of them except retail and and corperate
http://www.techist.com/forums/f9/many-versions-xp-188450/
Retail and corporate are the most common ISO's I have found but if he looks specifically for the OEM CD he should have no problem.
Also to the OP a lot of the "modded" versions out there don't work properly so if you find one that doesn't seem to work no matter how you burn it, it is not a good image file so you'll have to keep looking until you find one that works and the best way to save yourself the time effort and money of burning Frisbee's is to mount the image first before you burn it to see how it reacts.. if it gives the blue XP pop up as soon as you mount it.. that is a good indication of a good ISO image file, if it opens in folder view, it most likely isn't a good one.