FIrst of if your router is asking for a username and password for the connection then you are doing it wrong. Reliance is not a regular ADSL dialup setup. It is a captive portal based service.
I have a BSNL
Huawei modem MT841 which works fine (tho i am using origianl modem + router setup , cus its always better than standalone ones)
Try selecting a DHCP option, as i don't know what configuration options your modem asks for, i can't help certainly.
But try the following as in the image below !
http://imageshack.us/photo/my-images/708/ylmj.png/
Connection type should be sometime like : - DHCP, Automatic Configuration - DHCP etc,
Set VPI = 0
VCI = 35
these are the most basic settings needed.
If you still can't connect then post a screenshot of the configuration page where it has the adsl connection options!!
Good Luck !