Was playing about with the interface yesterday on my dad's 01 Passat TDI (OBDII compliant)
The interface used an rs232 chip, found the schematic from andywhitaker.com on one of the additional diagrams.
Used the VAG-COM software (found a crack to register it to get full functionality as well wink )
Plugged it in, worked fine with ignition on - could retrieve VIN no, loads of data - it read all the engine monitoring values but as the engine was not running, rpm, speed, air flow, etc stayed constant.
As soon as the engine was started, it lost connection. Switch it off - fine again. I had to enrol the help of my dad and a scope for this one - too much noise was being created and the signal was not properly grounding, anyway a few components later and it was sorted - it works
was reporting back all the info you'd expect, then went for a drive to log all the data, seems pretty comprehensive. The VAG-COM software won't work on the alfa's - the protocol the VAG's use is KWP2000 - the alfa's will use 9141-2 I think.
I tried the interface with the software from obd-2.com and could not get it to work - after further investigation I think that software needs its own interface - perhaps it acts as a dongle.
I could not find any other generic (free) software which would work with a standard interface other than the VAG-COM software.
I haven't tried this with mine (still waiting for my connector to come) but know it won't work - wrong protocol.
I am now investigating the ELM chip from www.scantool.net
This looks more universal as the ELM chip converts to ASCII, should be easier if you have to program something too.
EOBD is more advanced than OBDII, but uses similar protocols. Also OBDIII is in design stage....