A Mac Mini in a car better have some serious self-powered heating and cooling system! Not to mention its very own waterbed for shock protection!
Or maybe it could stand the extremes if the HD were replaced by a RAID of flash chips?
Anyway, I bet the project will draw an upsurge of interest from the Windows switcher DIY crowd too! Might even draw some new people into programming Mac software
EDIT: Yes, OS X voice commands can trigger AppleScripts, and iTunes is controllable that way. (Better yet, maybe, with Automator in Tiger.) Unless the music interferes
I see no iTunes voice control scripts ready-to-go in Panther. But wow, Address Book is sure loaded with voice control!