What OS should I use to run a basic home file server with 256MB ram?

I want to take an old system I have laying around and turn it into a basic file server for three systems (all running XP). I will put a 160gb hard drive on it and use it mainly to back up my media files and as centralized storage for all my music. It is an old Dell and only uses RDRAM. Currently, I have a 1.4GHz P4 and 256MB ram in there and do not want to pay the inflated prices to upgrade the RDRAM.
My question is this, what OS will perform the best for this application while running 256MB Ram?
I own full legit copies of XP, W2K, and 2003 server and prefer to stay away from linux (unless it is super easy and has a fully graphical interface). Your thoughts?
Thanks

For the longest time I used windows 98 for a box that was just acting as network storage and I had no problems at all. If you only run a basic setup 2003 server will work OK on 256MB of RAM, I had a P3 667 256 MB running it, and it was fine.