DO you actually plan to do the editing on the media server or simply pull the data from it to edit on another PC. In general all media servers are just that. They don't use very fast CPUs as they don't need to, they need to keep power consumption down to save money and noise.
Good point, Bob. If the media server is for storage, and the actual editing machine also has SATA drives, it "may" be fast enough, but not as fast as hooking a big drive up directly to the editing machine.
Network servers are known for sluggish performance under heavy simultaneous read / write operations, but I actually do this quite often for SD source editing and rendering.
I have a HP Mediasmart (WHS) used for storage of completed projects on a 1k network. Occasionally I have opened a veg and assocaited files stored there from my editing PC over the network and had no problem editing and rendering HDV projects.
I have an i7, 12 GB and win7 64 / Vegas 64 and am importing 30 min. of AVCHD files from my Netgear Ready-NAS frequently just to cut the ends of them, place a "local" intro and "outro" and then render.
I would not like to edit very much in the files when it comes to AVCHD I must admit. DV and probably HDV would be ok.
If you only by this mediaserver to be able to do this, I would try and see if I could do some testing somehow first. I use mine mostly for archiving cutaways, pictures, intros, outros, renders etc. that I use on different PC's all the time.