Router/Gateway needed for Asterisk remote location

Hello all.  I am trying to setup a Ununtu Linux box as a gateway/router running Asterisk to my office Linux box also running Ubuntu Linux/Asterisk.  I need the Polycom IP phones to connect remotly to the office Linux box to receive and make calls.  The office system is a fully functional working system using the Polycom IP phones.So far I cannot get the phones to work at the remote site routing through to office computer.  They are fully functional at the remote site.  I have tried to set up a gateway without any success and tried some routing configurations, again without any success.  Help would be appreciated.  The following is my current remote location configuration.1.  The remote site is connected to DSL via a Westel Wirespeed modem2.  The Westel Wirespeed modem connects to a D-Link router lan port 1.3.  The WAN port on the D-Link router is not being used.  4.  Port 1 of the D-Link router is attached to the Westel Wirespeed modem.5.  Port 2 of the D-Link router is attached to the Ubuntu Linux box. eth0:  A second ethernet card in Linux is available but not set up at this time.6.  Port 3 of the D-link router is attached to the Polycom IP phone.  Port 4 of the D-link router is attached to an XP Professional client. you in advance for any assistance in this matter.