I am going with an AM3 Board(Gigabyte GA-MA785GT-UD3H) with 2GB DDR 3 Ram.
Now am down to choosing between 2 processors
AMD #140 AM3 SEMPRON 2.7GHZ - 45Watt
AMD #250 AM3 ATHLON II X2 (3.0 GHZ) - 65 Watt
I guess the question is... is a single core 2.7GHz enough? Using the #140 would save ~$75 and also 20 watt heat/power.
It is likely I would run torrents/downloads directly on the WHS.
For simplicity's sake since I am trying to keep heat/power (and to some degree cost but wont sacrifice quality) I have picked the fastest AM3 45 watt processor and Fastest 65 watt processor and am ignoring the other processors in between