If you want to share files with Windows easiest way to accomplish it will be Samba. You can find Samba in FreeBSD ports (
ports/net/samba36/). Samba config file is well documented, and there is a lot of examples, so it shouldn't be a problem to create shares that you want. You can also use SWAT, which is web interface for administering Samba.
If you want to move files from server to clients (or in the opposite direction) only from time to time I will use ssh. Only thing you need is to install ssh on server and some clients on other machines. For Windows you can use WinSCP, on other systems
scp file user@server:/path from command line or some graphical file manager (Dolphin in KDE, mc on console (menu of panel -> Shell link -> user@host:port -> OK)).