I've got the interface sold at

http://www.obddiagnostics.com/

and can tell you it works great on my 1996 S500. Also, works fine on all my Fords, my wife's Lincoln, etc.
Nice thing about the software ... not only is it free, but you can download and run in "simulate mode" so you can try out the display before buying the interface.
I've run the software on everything from a 50Hz 486 to a 500Hz Pentium III. Works fine. Display is nice and large; easy to read. Also allows you to plot O2 sensor performance and mixture trim.
Nice.

Hope this helps, KenP