One more for the nerds...

Underclocking. I have, simultaneously, a need desire for a low power always-on server, and a spare old gaming machine. The gaming machine is currently overclocked to something silly, but it's still not as grunty as my more modern workstation from China. If I underclock it, i.e. reduce the core voltage, will power consumption go down? I think it has built-in graphics, so I can take out the old card, and modernise the drives.

Or should I just drop ~$200 on a modern Atom integrated board and 4Gb RAM?