I did similar setup with a ELM327 USB Interface OBDII cable from ebay and the software loaded onto my Pioneer DD head unit itself.
Was ok but grew tired of it and now just use the cable and my laptop when needed.
But for those interested:
Cable:
ELM327 USB Interface OBDII OBD2 Diagnostic Auto Car Scanner Scan Tool Cable V1 4 | eBay
Software:
hobDrive - OBD-II trip computer for Windows Mobile, GPS devices and carputers ? hobDrive
Hack the Pioneer head unit to allow quite a few added features which includes the OBDII hack via AVICnet.
AVICnet 2.1 for AVIC F series, working OBDII! Updated 04/18/12 - Completed Mods/Themes - AVIC411.com
