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: