It is an adapter that you plug into the 12V cigarette adapter in your car. It has a box that then comes off the cable with a standard 3 prong plug on it, letting you plug any home power adapter into it.
Check this one out to give you an idea. This is way more wattage than you need, but it does have dual plugs, which is nice.
You plug this thing into the cigarette lighter in your car (or whatver you have). Plug the cable in. This cable is attached to a brick that has a fuse and usually 1-3 outlets. These outlets supply enough power to run your computer and you just plug your power brick from your computer in to it and your set!
Okay, I looked up what a power inverter is . . . and feel like a total idiot! I could have bought one power inverter instead of all those different car chargers for every gadget we own! Okay - lesson learned. Never again.