power for a DC-DC power supply to handle.
intellegent automotive PSU" (which is a DC-DC PSU with a built-in startup/shutdown controller).
wiring required to provide power to your carPC is very basic and easy to learn/understand. you're doing the right thing by asking questions now (as opposed to just "winging" it).
remember two important things before you buy/install anything. most important is; you MUST fuse your wires as close as possible to the power source. your main power line should be fused within a few inches from the battery, and anytime you reduce the wire size you should use a [smaller] fuse at the beginning of that line. the other important point is; your wires must be thick enough to handle the required current (amperage) draw and to minimize voltage drop. the wire gauge and fuse rating will be specific to your system, so we can't suggest anything until we know what you'll be using.