ok, well i dont beleive i have any OEm apart from the restore cd's i have gathered from repairing other people PC's

i must admit i have vista home pro OEM and i've changed harddrives 4 times! no problems so far, also i've upgraded the ram and still no probs.

i must admit i'm currently working on building a completely new pc using the intel core duo and i was going to use the same vista oem os i'm using now, so i dont know if that would be completely different.

i'll let you know if i run into problems.

having said that i did upgrade an old pc with a new mobo and cpu, with it i completely reinstalled XP home (which again was a OEM version)

once i started installing it i entered the validation number, using the phone number that came up on the screen i entered the code given.

A problem did occur (due to the hardware change) i was prompted to speak to a microsoft technician which i did i then explained to them that i had purchased the original pc from pc world years ago and just wanted to use it on another pc instead. without a batter of an eyelid she gave me a new code which validated the software and that was that, no problem.

just thought that might help.