For power, there are two ways to go: DC to AC inverter (provides house outlet from cigarette lighter) and actual power adapter for that Dell that plugs into the lighter. The Dell adapter is a better choice if you want to keep the buzz out of the audio.
For mounting, there are a number of console and floor mounts out there that provide a solid mounting surface. As was suggested to me for a 15" LCD, think about how the cops do it! They already use Motorola "ruggedized" laptops in their cars, so the hardware to mount one should be pretty easy to find on the web.