You guys are not understanding what VIDEO EDITING needs are.
He is not primarily using this box for XVID, DIVX encoding. Editing and encoding are two COMPLETELY different things.
He will be slicing and dicing clips of video, composing, rendering, effects handling etc. and outputing to a standard format where the fastest drives and Xeons rule by far.
Only during that last output conversion will the encoding part come in which is not disk intensive. Most likely he'll be working in various mpeg formats as well as DV stream. For this purpose, Xeons with tons of memory and fast SCSI drives RULE.
It is also quite a bit cheaper than Opteron. What is he going to do with a 6800 SLI rig with no realtime effects handling, lack of hardware encoded capture and limited physical output jacks? It's not going to help AT ALL. Zilch.
Also if Apple's Finalcut Pro looks like a good software package for you, get a Dual G5 and a Matrox RT series board or again a Canopus. I've got a client who handles editing in big time commercial cuts (Britney, Blueman etc.) with Finalcut and a dual G4. It's not trouble-free but she gets the job done on time with me there.