Firs of all, download the Z600 driver from this link http://downloads.lexmark.com/cgi-per...e=&fileID=1242

Extract the file and rename it from z600cups-1.0-1.gz.sh to z600cups-1.0-1.tgz.

Open it with your favourite text editor and remove the script from the begginig of the file.

Extract the tar and convert the two rpm packages whit alien ("sudo alien *.rpm")
Install both packages whit "sudo dpkg -i *.deb" and you got the driver installed.
Finally install it with the gnome printer dialog and select Lexmark -> X600 1.01 driver.

Enjoy

NOTE: I had to restart gnome before installing the printer.
NOTE 2: Sorry for my bad english