IBM 73P0595 Rev 2.1 Socket 478 Motherboard 3GHz Pentium 4 2x 512MB Windows 98 XP
I went with 2 x 512MB sticks of RAM, as that way you can just remove one if you wanted to run 98, which doesn't like more than 512MB of RAM. If you want a little more grunt, you can always put an AGP graphics card in.