I have been tasked with setting up a new media editing PC (photo and video) for our marketing department. I'm very familiar with all the hardware, but I don't know quite as much about 'workstation' vs 'normal' machines from vendors.
In this particular case, I've been told to order from Dell since our company has a business relationship with them already. I've noticed that I can get much newer and faster hardware in an XPS for a significantly lower price than the Precision line, typically in the $500-$800 range. We are a medium sized company, so that definitely makes a difference.
From what I read, it seems that the Precision is suppose to be higher quality hardware that can take more use / abuse. While the machine will be in an office environment and powered on most of the time, it will only really be pushed heavily to edit and encode...