Try Vista or Server 2008 on one or both of them? It would be interesting to see how it performs on machines close to its minimum official specification - you'll need at least 512 MB Ram to be able to install Vista or 2008 (so the AMD is in, and the Intel too if they use the same type of memory and you can swap it over), and the processor requirement is 800 MHz but I doubt that MS are as bad as Apple and put blocks in to thwart installation below that, so the AMD should hopefully still be good to go. If you have a reasonable graphics card (DX9, plus I think it needs 128 MB+ of memory) you'll even be able to get the full Aero interface.