Get BSD man...it's the only way to go with servers. If security is not an issue get FreeBSD. I promise you'll love it If u have low end computer (like pentium 100 or so) get NetBSD. NetBSD is more complex, but rox on lowends.

BTW u should get FreeBSD 5.1 (it has a lot of new great features, like UFS2 and such)

I agree. FreeBSD r0x! I have 7 fileservers on my home network, and I typically recommend/install FreeBSD servers for my clients. The only thing you need to install (besides the networking stuff) is Samba.

I also have a few Slack servers running around somewhere, but they're mainly DHCP/DNS servers that are in desperate need for upgrades (one I think is still running Slack 3.6).

FreeBSD is very easy once you get past the install, which shouldn't take too long to figure out.

When you're asked if you want to install the "ports" collection (during install) answer YES. Then, to install a package, you cd /usr/ports, cd into the directory that contains the package you want to install, then simply "make install". FreeBSD also checks your dependancies before actually installing the package, so if there's something it needs that you don't already have, it fetches the files, compiles it, installs it, then continues on with the original package (much like Debian's apt-get, but no more guessing the names of the packages you have to get, because they have their own directories.)

If you get stuck, you can check out the online FreeBSD handbook, located at http://www.freebsd.org/handbook

If you are looking for a fileserver, samba works best with linux. But if you are looking for network services (apache) or network services (firewall, NATD) FreeBSD is your choice. Awesome sysctl control like:
kern.ps_showallprocs=0 disable user from viewing other's processes during 'top' command.