Adding a Mac mini in a Corvette, and turn it into the media central unit featuring a 7" touch screen display: this is Andrew's project, extensively described in his blog. Of course, you might miss the Corvette, but any other car could be also used.
You will need an power unit from Carnetix, a bright touch screen from Xenarc, Front Row Remote. One could also use Xamp, based on AMP(10.4 MB), a SourceForge project.