i'm planning on building a desktop computer (well motherboard and video card) into the trunk of a car for a custom built navigation and music playing system. (yes, i am worried about heating problems, but i'll worry about that later on...) Is there an ATX style power supply that uses 12 vdc as the supply (rather than 120 vac)?

Also, the computer will be in suspend mode (hard drives turned off, no fans) when the car is off. how fast will this drain the car's battery?