- Uninstall the printer, if already installed from a previous version of OS X, or from previous attempts to install Lexmark's drivers
- Open Finder, click on your HD, find Library/Printers/Lexmark, and rename it to Lexmark.bak
- Insert your Leopard DVD, double-click Optional Installs, double-click Optional Installs.mpkg
- When Optional Installs has loaded, open Printer Drivers, and check the box next to Lexmark, then finish the installation process.
- Open System Preferences, and then Printer and Fax
- Click the + sign to add a new printer
- Your P4350 should show up as "4300 Series Printer" in the list. Select it.
- The dialog may spin for a few minutes. When done, it will enable the driver selection list. Select "4300 Series" from the list and click OK.
You should now be able to print. I did this on two different Macs, and it worked for both.