Ideally I'd like to turn the screen off too to save power!
Right-click on the Power Icon in the systray and select Power Options.
Look at the available Plans. Select Change Options for the current Plan.
From here you can set how long the computer waits before it turns off its display and how long it will wait unattended before it hibernates.
I'm not sure where the setting would be in Windows 7, but on my XP laptop in the power saver settings you can change the behavior when you close the laptop. Just tell it to stay on when that happens. I believe it should still turn off the screen, but otherwise it will stay on.
Just make sure you have the laptop plugged in.