After trying Windows XP Pro, Windows Server 2k3, Fedora, Ubuntu, Arch Linux, NetBSD for the file server OS.... They all had their ups and downs.
Win 2k3 although was only a trial OS because the full one is really expensive. It took a bit to set up due to my complete ignorance with Win2k3. Although got it in the end (apart from NFS and one or two other things). I got 180 days before it expires...
Fedora Core 4, easy set up, quick, most things done with point and click (GUI). Got samba up and running fast, NFS, FTP and web server without too much hassle. Had a few problems initially but due to its large support base there is usually hundreds of people who had experienced the same problem. Now for the downside, it is a bit bloated and slow. Also not a fan of RPMs, and they way Fedora does things differently, like where system configuration files are.
Ubuntu, good rock solid distro with the quickest setup time. But for some reason I just do not like Ubuntu.
NetBSD, a bitch to set up, never finnished setting it up, could not be bothered... Apart from that it was rock solid, none of this GUI crap...
Arch Linux, awesome simply awesome.... A bit of effort to set up but nothing too hard.
Windows XP Pro, now considering the server is usually open to the outside world (although it was sometimes) with this I also streamed TV to the entire house using VLC with its multicasting capabilities... As the VIVO of my video card works well with winxp. As for NFS (clients are mostly Linux, NFS > smb) tried to set it up, failed so far, but will get it eventually.
I use VNC and ssh for remote configuration.
Hardware I use WD 300GB sata, Maxtor 250GB, and soon a Seagate 500GB...
Asus A8N-SLi Premium, also to network everything togeather I have a Cisco 837 ADSL modem /Router.