First, there are some generic drivers that are included with OSX. If you didn't throw them out to save space (as is often advised), what comes up under System Preferences > Print & Fax > Printing?
Assuming nothing included or suggested works, write Lexmark and tell them how much you like their printer and how sorry you are that they don't support yours under OSX. It appears that Lexmark no longer makes the 3480 but they bothered to write a Vista driver for it. At the very least they should know that not supporting OSX has consequences.
Finally, it's just a $90 printer. You can get a perfectly fine, and compatible, all-in-one printer from HP or Epson for the same price. Why support a company that doesn't support you? Best wishes.