Well active directory which basically is Microsoft's domain system is overkill. And, sure you don't need Exchange, but when you have it is nice. Mainly for the fact that you can email within the office, and it doesn't go over the net, and RPC/HTTP (which I don't expect others to understand -- I CERTAINLY didn't at first) is awesome.
But, I was mainly referring to don't go looking to buy an NAS or something like it to run your AC. You may as well save up and get real server or even a souped up XP or Vista.
