For those interested, a quick update:

I picked up an Elmscan 5 from the local distributor about the middle of the week, plugged it in, and it worked great. It detected the car was running a CAN protocol adhering to the European OBD version of the standard. I'm getting a range of sensor information, from the usuals (RPM, speed) to absolute throttle position, engine load, manifold pressure, mass air flow, O2 sensors, coolant temperature, air intake temperature and quite a few others. I think I can get enough information out of the car to calculate things like instantaneous and average fuel consumtion in real time, though I might have to try my hand at altering a program like OBD Gauge if I want a proper trip computer.

It seems that most of the software out there is fairly basic. I ended up buying PCMScan as well because it offered data logging/playback and seems the most feature rich for the moment. It's been a fun project so far, and started me thinking about a carputer project (like this one). I can dream.