I use the computer too much, do you?

Sit up properly. Good posture affects more than just your back, you might well find the benefits extend to your legs and arms too.

Also, use more keyboard shortcuts so you're on the mouse less, although you didn't say exactly what it was you do with computers all day.

I'm on the computer pretty much constantly at work which can be as much as 12 hours a day lately, and then usually another hour at home. I mainly use Excel and Sage though which is primarily keyboard work rather than mouse stuff and my wrists and fingers are fine, despite the fact I'm a terrible slouch when I sit at my desk. I also have the mouse sensitivity turned up ridiculously high so I barely have to move my hand to cover the whole screen. I don't really move my wrist at all when I use the mouse, just hold the thing in my fingers and there's enough movement there to get to anywhere on the screen.

Edit: I just measured it and I never move the mouse more than 2cm in any direction, which I would think helps reduce the risk of RSI.

Jam it back in, in the dark.