Hi rwrd, It sounds very much like the person who purchased the device did not get the Postscript interpreter. If this is the case there is no driver that will give you full functionality as there are only PS drivers for the Mac. And while OSX has a Generic PCL that will get it to work, all options like the finisher, extra trays, mixed media, staples,folding and Accounting will all be missing..
You can verify if the printer has a PS interpreter by verifyingit shows up her ein CWIS. (Centreware Internet Services)
Properties>General Setup>Configuration
If that is indeed installed, we would need to troubleshoot what is happening during the driver installation, If that does not show up, you need to get in contact with your sales agent, the Postscript interpreter is not free as there is a hardware board that is added along with the software that runs it.