To set up power settings you can do this in the control panel goto
Start-> Control panel(If useing XP display and Themes) if not Display-> Goto the screen saver tab. You will see a Power star management system click advanced.
Here you can set the time durations of how long your stuff stays on after idle
Set your monitor to 20mins
Goto Standby and set it for like 3 hours or so this will shut down everything on your computer when you hit the space bar your PC will start back up where it left off when it went into Standby.
you can also set Hybernation This will shut everything down and store everything in memory powered by the CMOS battery in your computer. You will have to hit the power button to start it back up but it also saves on your computer..
So I hope this helps ^_^