Low power media server

Getting a new Core 2 Duo laptop that should run circles around my desktop.
So I'd like to start using the laptop as my main PC and make a small media server to store in a closet somewhere and access media from.

Anyway, how would I go about creating a low power server. I couldn't care less about speed, as long as it can transfer MP3s, videos, data at a good rate.

Specs of what I have now:

ECS NUsomething (Nforce 2 chipset)
AMD Athalon XP 2800+ (2.0ghz)
1GB DDR
ATI 9600 128MB AGP video
5 HDs = .9TB of stuff.

My laptop I ordered will be:

Intel Core 2 Duo 1.6Ghz
1GB DDR2
ATI X1400 128MB dedicated+up to 128 shared
60gb sata 5400rpm


So I figure the laptop should be far better than my desktop for everything.

What can I get to make a lower power desktop server. I have access to like a P2 or PIII desktop also.

Anyone? Thanks