Ques. I want to use d-link dir 505 as a repeater to my MTNL wireless broadband modem to extend the wifi coverage to the study room 20' away from the present living room. How to configure? Should this be done by going to MTNL?
Ans. MTNL will not configure this for you as it is not their product. You can configure it yourself by reading the manual or using the cd that came with it. All you need to do is set the dlink in the "wireless repeater mode" . Set the SSID and password of your existing wifi connection in the dlink 505 and it will start transmitting the signals of your Wi-Fi to your study room.
Installation instructions can be downloaded from here : http://support.dlink.com/ProductInfo.aspx?m=DIR-505