I recently got 100mbit internet at my place, And now i'm thinking of building a small file server for myself.
My thought is that this server also should run the Airvideo server software.
Airvideo 3.0 is probably around the corner with 1080p,5.1 etc.. and with that higher bit-rates!
Right now im on a core2duo@3500mhz with 4gb ram, and with the highest settings the computer is really maxed out serving hd material..
Well, I would recommend quad core with hyper threading, however the benefit of Air Video 3 will be that in general less videos will need to be transcoded. Although the really high bitrate videos or high 10p videos that can't be natively decoded by iOS devies still will need to be transcoded.