Im using a mII6000E
600mhz fanless mini itx and it does gps dvd movies mp3/ogg/mid/mod etc and it plays snes nes c64 megadrive(genesis for u usa folk) sms game gear gameboy gbc gba and mame.
And this motherboard does all this plus wifi
300mhz with GPS is the lowest system we have seen so far but i reccomend 400mhz as bare min.
But you will add more very soon to your project even if u just use it for gps u might play a few cd's
but i only use GPS and mp3 the movies and games are for the passengers altho i wont have any as its a sports car its there just in case