I didn’t realise it was possible… and it’s really very easy!
In windows (I’m using 98, and I think XP has better options), go to control panel, and power options.
I set mine to turn the monitor off after 5 mins, the hard drives off after 15 mins and the system to standby after 30mins. We’ll see how we go with that – might have to set the times for hard drive and standby longer….but I’m constantly going off putting a load of washing on , or dealing with an order or something, so when I’ve gone off twice this morning I’ve come back to find the monitor off – just wiggle the mouse and it comes back on. Means no need for a screen saver either!