As of Ubuntu 14.04 (and earlier versions):

If you have a 64-bit system, copy and paste this into the Terminal (open it with Ctrl+Alt+T) and press Enter:

sudo apt-get install libcupsimage2:i386

If you have a 32-bit system, ignore that terminal command and proceed.

Download the Ubuntu .deb drivers from Xerox for their Phaser 6000 model. It comes packaged in a .zip file. (The Dell C1760nw is a "repackaged" version of this model, which means that the core printing device works the same as a Xerox Phaser 6000 because it came from the same factory, but it is assembled and sold to retailers by Dell instead of Xerox.)

You will need to save this .zip file, and extract its contents with a right-click if you are looking at it in the File Manager. A folder will be extracted, and therein will be a .deb package file. You should double-click this to open it.

You may encounter a window saying that the package is of "bad quality". You can safely ignore this; it's coming up because of an incorrectly entered variable that declares the creator of the file.

Then, install the printer. If you are prompted to choose a printer manufacturer and model, enter it as a Xerox 6000b. It works!

Note that all of these steps are still required to use the printer over the network.