solution for Lexmark x502n with snow leopard 10.6. on an ethernet network.

Go to System Prefs.

reset the printing system

1. Control-click or right-click a print queue in the "Printers" pane.
2. Choose "Reset printing system..." from the contextual menu.
3. Click "OK" in the "Are you sure..." confirmation sheet.

this will erase all your printers.

Install Lexmark_X500_Series_X-1.dmg [available at the lexmark website]

go to print & fax prefs in system preferences and add the lexmark printer as an IP printer with it's IP address. Protocol should be set to LPD. Address is the IP address. Queue is blank. Name is your choice. Print using the lexmark driver.

This worked for me. Amazing.