Connecting a 3COM Officeconnect 11g WAP to my ADSL Modem/Router

I have an ADSL Modem/Router at home with three wired PCs attached. There is a spare ethernet socket left for a fourth computer.
I have recently got a laptop with wireless connection in it, so I can use it without being wired.
To add wireless to my ADSL Modem/Router, I got hold of a 3COM Officeconnect 11g Wireless Access Point, to be connected to the last ethernet socket I have.
I have plugged it into this socket and configured the wireless, however, I cannot seem to get access to the Internet through the ADSL Modem/Router. What do I have to do to make this work?