Unfortunately the printer driver for my NEW Lexmark X5470 will not work with Leopard. I'm hopeful they will update the drivers soon.
Open System Preferences:
Click Print & Fax:
(If there's a printer already added, remove it)
Click on the + sign on the bottom left:
Select the printer (and optionally give it a shorter name), click the "Print Using" section and select "Select a Driver to Use":
Almost at the very top you'll see two "5400 series". I've chosen the first one, but I don't know if they're any different. Click add, and you should be shown a nice little icon of your printer:
Then I suggest you re-install the software from the CD that came with it to access all the features.
If that is what you've done, and you feel like I'm patronizing you, then I apologize, but those are the steps as I did them and I've not run into any problems.