Currently, all Dell N-Series Precision Workstation desktops are available and supported with Red Hat Enterprise Linux. For help running other Linux distributions on your Workstation, you might consider posting to or viewing the linux-precision mailing list.
Dell sells select desktop and laptop systems with Ubuntu Desktop Edition factory installed. See the wiki for technical details.
Dell sells some "n-Series" Desktops, Workstations and Laptops. "n-Series" systems ship with FreeDOS on a CD in the box.
There are many "community-supported" resources available to help you get Linux running on your desktop or notebook. These links include:
Dell need to expand client-side Linux support. The split-brain between the server division (who have to support Linux) and the client-side division (who seem mostly not to care) is dumb.
The Sputnik project is a great start; now expand it to the rest of your laptop product line, please. The hardware in my XPS12 is great, but it sucks that a) I have to buy a Windows license that I'll never use, b) I had to restore Windows, run a BIOS update, then restore Linux again; c) I have to go digging using lspci, dmidecode, the Web etc to find out what the hardware is in order to find out how to configure Linux to best run on it. I could go on but it's probably best I don't.