You'll need a motherboard like this one:
What is your budget for this system? Also, just so you'll know, you don't need a Xeon for a video workstation. Pretty much any modern AMD or Intel based PC (or notebook for that matter) can perform these tasks.
under 1000$. preferably 800 or below. i work in programs like After effects, sony vegas, and cinema 4d.. if that helps any,