Home Edition and Pro COA Question

Working on an older Gateway desktop ES2 300x 2.1G rig. Purchased the unit new from Gateway a few years back and it came with OEM XP Home edition. I am trying to replace the HD and load a fresh copy of XP Pro retail (don't have Home retail on hand or even the OEM on hand). I have a valid COA key for my Pro but I keep getting "invalid Key" when installing.

I have read in microsoft KB's that OEM keys can be embedded in the mobo's. Never heard of that but whatever. My question is, if this is what's conflicting with my "fresh" install then is there a way to clear out the OEM key or should I try and get Home edition and use the COA on the box currently ?



Thanks