Uhm, I'm surprised that no-one has commented, however I'll continue updating this thread with info as I find it...
Seems like Elm Electronics has written some software to convert from ODB protocol to RS232 ASCII making interfacing rather straightforward; therefore there seems to be a reasonable selection of freebie software already available for ODBII systems.. see below...
However, I still don't see anything (bar Carsoft) that fulfils the pulse code output of pre '96 cars & ODB (something) coming from the LH ECU. I guess it's a VERY limited market so no one bothers!
Elm Electronics ODB protocol to RS232 ASCII uC
http://www.elmelectronics.com/
Hardware + freebie ODBII software
http://www.scantool.net/software/scantool.net/index.shtml#translations
Regards
Lea