That won't work. If you enter someone else's key the computer will recognise it (online) as belonging to an already-installed version. You'll have to phone Microsoft to sort that one out.
Like the others say: product keys are all different.It's to prevent copyright, piracy, etc. So all serial codes for Microsoft products, games, etc. are all different and usually once they are registered...Microsoft will not accept the same code ever again.It's their way of protecting themselves and getting as much money out of you as possible.G.W.K