I Had a Linksys WRT54GS v4 running DD-WRT all the info you need is here http://www.dd-wrt.com/wiki/index.php/Switch
LAN card > 192.168.5.1/24
WAN card > Public IP from Virgin Media SuperHub Modem
But i have only config it using a wingate proxy server (Similar to pfsense) but it should work good with pfsense
;)