Why, that's a PostScript Printer Description file - something we don't usually have to worry about on the Mac. Mac-friendly printer drivers tend to hide the PPD deep inside the driver package and let OS X figure it out. But lacking an official Mac driver, you need to add the PPD file to the Printer Setup Utility manually. Download the PPD file for your printer from www.linuxprinting.org and stash it somewhere on your Mac. Now fire up Printer Setup Utility and click the Add Printer icon. Your connected printer should appear in the Printer Name list (if it doesn't, click More Printers and select AppleTalk from the pull-down menu). Select it and proceed to the Print Using dialog. Select Other and navigate to the PPD file that you downloaded earlier.