Based on your requirements you dont even need to think about which linux distro - if all you want is to turn it into a file server for your local wan try an appliance called "freenas"...

I have an old sony viao pc running it - upgraded it to a 1gb net card - and everything in the house (pc/windows, pc/ubunto, imac, n800) all work with it.

Simple cd boot, install and fconfigure/format drives with a web gui and you are on your way. 1/2 hr investment tops...

My 2cents.

(oh yeah - and its still unix - just bsd under the hood and you never need to see it if you dont want to).