Set it up and point your services you want to authenticate against it to your server?
Maybe you should start by telling what you're trying to do because there is no such thing as
"how to setup TekRadius (www.tekradius.com) to communicate and work together to pfSense?"If you're looking for help with TekRadius: this is the pfSense forum and you should look for help on the TekRadius help channels.
This is not a forum about Windows Server 2003 but you can find information about how to combine it with pfSense.
See: http://www.pfsense.org/mirror.php?section=tutorials/cp_config/radius_win2k3.htm