The Dell 720 is a rebranded Lexmark z615. If you have not deleted your complement of preinstalled drivers, then the driver for the Lexmark version is on your computer. If not, then you can download the current driver from Lexmark.
I downloaded the lexmark program and it couldnt find the printer as I was going through it. Maybe I'm just a moron? Maybe it's because the printer goes through a powered hub? Maybe I'm just an idiot? Did anyone get this working?