A company that I consult for has just upgrade dall their dells. This involved dumping loads of XP disks. None of them had the COA as they were stuck on the base units. I would suggest that you have be sold a pup. the wording of the Ebay advert is very important and you need to read it carefully...did he advertise an XP disk or a disk and COA. In any case I would nail him pronto.