Johnpr: there are two options. The scangaugeII will work on any OBD II car (1996 - present) and then there is the SuperMID which works on OBD I cars (pre-1996). I know you can get the scangaugeII just about anywhere. I found them on Amazon and Froogle.com for around $150. The SuperMID I have heard is a custom product that is out of production right now, someone correct me if I'm wrong, but I have no idea how to get one of those.
Look them up,
www.scangauge.com