Enable Wifi Access using Belkin F5D7632-4 v1000uk ADSL modem with wireless G router

Hi All,I have searched the entire forum but I am not able to enable wifi using Belkin F5D7632-4 v1000uk ADSL Modem with Wireless G router.Most of the post which I have gone thru talk about a ADSL modem and a separate Wireless Router. Unfortunately mine has both the modem and router built into one. I have BSNL Dataone unlimited plan. My home setup is Ubuntu 9.10. I am able to connect to internet using the belkin modem only if I choose "No Internet Sharing" option of the modem setup. If I choose Bridge mode or PPPOE mode the modem says not connected.Can you please help me. I want to enable internet sharing over WiFi using my modem.