Also, I had the same problem finding the driver on my harddrive, so try looking in /usr/share/cups/model after you complete the tutorial. In that folder there will be a .tar.gz with the name Lexmark-z600-lxz600cj.cups somethingorother. Right click and extract it to that folder and it will turn it into a .ppd. That's the driver you use in the printer setup.
Hope that helps. I'm a newbie myself, so I have no problem batting back and forth with solutions.