Motherboard bundles from Novatech click here are frequently recommended on this forum. I think this is an excellent route if you're not 100% confident in specifying the parts yourself. You could possibly get cheaper by shopping around for the individual parts, but you would probably also end up paying more for postage. For general home use you might find that it isn't much more expensive to buy a ready built base unit - but it wouldn't be nearly as much fun. If your old computer has an OEM version of Windows XP installed, you might have problems with using it with a new motherboard because it will be registered with the old setup.