lower power usage?

I got a problem here.
In my house my family just got a ton of new computer systems. 6 desktops in total, with three of them being dual CPU systems that eat up a ton of electricity. One of those dual CPU systems is mine, and it probably uses up more power than any other system in the house.
The power bill just came in and it was around $400, so the computers can no longer be running all night downloading, but I also can't max out my torrents during the day cause people actully use the internet at my home.
Is there any way to lower power consumption and still download the torrents?

>>5
Same person. Have you thought about picking up a cheap computer (or using an old computer) for downloads? Or even for general use? I don't know why you have 6 workstations for 'family computers', but even if you have a business or something that requires them, you could use a non-workstation computer with a C2D for most purposes and it would consume significantly less electricity.