100W under what load? idle? web surfing? folding?
FWIW I just bought a Kill-A-Watt and have slowly been measuring many of the power hogs/vampires. So far my Dell tower wins (or is that loses). At the UPS It consumes 110 W while completely idle. That goes up to over 240W if I'm doing something CPU/HDD intensive like compressing video.
I have yet to connect it to my iMac, but I'm seriously considering replacing the tower with another iMac/mini just to be able to let the stupid thing sleep reliably, something which I have yet to find a Windows box able to do gracefully.
B