Unless one of the 3rd-party driver sites such as GutenPrint <http://gimp-print.sourceforge.net/MacOSX.php> or the HPIJS Project <http://www.linuxfoundation.org/collaborate/workgroups/openprinting/macosx/hpij s%23Printers> has a driver which works with it, and odds are that they don't, you'll only be able to get a Dell printer to work with a Mac if you can work out which Lexmark printer it is that Dell rebadged
and if Lexmark supports Macs with that printer
and if the Lexmark driver works with the rebadged Dell. That's a lot of ifs.
Dell support and Lexmark support will
NOT help you get that printer to work with a Mac. Apple
can't help you, they don't have any drivers for it.
My suggestion? Get a new printer, one which works with Macs out of the box.