More information is probably going to be needed as to how everything is hooked up currently.
Thread moved to the newbie section.
I think your understanding of a DC to DC PSU is a little off. It sounds like you'd be better off finding an automotive adapter for your netbook and an automotive adapter for your lilliput. Everything else you listed should be powered off either the PC or the car's 12v directly, depending on which products you have. Once you throw in an actual desktop-style PC, you'll need to start looking at DC to DC PSUs.