I second the notion that the version (ie home, pro, ultimate) doesn't matter, all they do is add features you probably won't use in a mame cabinet. The choice between 32 and 64 bit is what is important, so if you can get 64 bit in the basic version, that would probably be the smartest choice. Keep in mind that finding 64 bit drivers for older hardware can still be a chore, especially on "OEM" computers like Dell or HP. Sharpen up your "google-fu" before starting a project like this, you will need it.