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?

It's probably not your computers because I have two computers both with a core 2 duo and it runs at around 25W (idle) to 69W (when doing CPU intensive tasks). Where I live it costs 8.5c/kWh. I keep the computers on 24/7 and it usually costs me less than $5 for the entire month for each computer. My power bill is around $150, but that's for other reasons.