Saving Power

Doing a bit of working out, I've found out that my PC if left on 24 hours uses around 5units (kwh) of power with the monitor and speakers on which is costing around 55p(80c) a day and driving up our electricity bill. I was wondering if you can get low power modes that, if I was to leave it on unattended that would mean I would still be downloading from BT and IRC would stay connected etc?

I've already got the monitor set up for power saving

That sounds a lot like Intel's SpeedStep system, where it'll underclock the processor to save batteries if it's not running at 100% CPU load. I don't know if anyone makes a such thing for desktop PCs, but you can achieve similar results by underclocking your CPU manually by 25-50% and disconnecting peripherals (especially ones with moving parts, like hard drives and CD/DVD drives) that you don't need. (I'd also suggest setting your hard drives to power down after a certain amount of time, but you mentioned BT so I don't know if that'll work well for you).