FreeBSD is probably one of the most stable operating systems around, and as such is extremely well suited for server applications (web, email etc.). I manage a few *BSD servers and once configured and running properly they don't cause any problems.
Setting them up is easy enough too (even for beginners), all you need to do is follow the install guide on freebsd.org and you won't go far wrong. Really the only prerequisite for installing is the ability to read. ;-)
Also run a couple of Linux boxes too. Even though both systems are different, the end user once up and running really won't notice too much difference unless they start to dig. The major difference people will probably notice though is the different methods distros have of installing software. Good examples are Portage (Gentoo) and apt-get on Debian.
