Buddy look up a very good thread on powering and turning on/off a laptop. I only have a small car too and was gonna run an invertor but am opting for a Dc-DC (get one from radio shack or ebay or summit but get a decent one). DC-DC is more efficnet and will not need a noisy fan. Xenarc can run right off battery (use a fuse!!!!) but it maybe best to use anothe regulator for it but at 8-10Watts this aint gonna be much trouble (a cheap CD player reg might work). I was usig an invertor to charge my phone the other day in my mates car and the Maccy D's cokes fell over in the foot well and i suddenly thought Sh******t - mains! Not really a big fan of having it in my car to be honest - its french so it will probably leak at some point!