Carputer power button wiring

I need to know how to hook up the power buttons for a carputer the right way. I need the ability to:

Safe power-up when the car turns on
Safe power-down when the car turns off
Ability to turn the carputer on when the engine is off.

How do I go about doing this. I am really only concerned that the computer safely shuts itself down after the  car has been shut off . I do not want to drain batteries or destroy computer components.

If this is too complicated, I will just mount the computer power/restart and monitor power switch somewhere in the dash. That way after I get into the car I can turn the computer on (no point in autostart if I am just moving vehicles) And then turn the computer off before leaving the car. I just dont want to forget to turn the computer off and have it continue to run and drain my battery.