i have my Night Owl DVR in the living room but my internet modem is in study room connecting to my computer. I brought this ASUS RT-N12 3-in-1 wireless router and try to use it as a wireless bridge for my DVR. Can you please guide me how to set it up?
You need a device supporting "Wireless Bridge" functionality, and as per the specs, this device supports "router", "access point" and "repeater" modes. Try "repeater" mode, if you're lucky, you'll get Internet access on the LAN ports - page 15 of the manual suggests so.
Important note: I truly believe that what you call "Internet modem in my room" is really a router/gateway, and not just a modem. Modems allow for single device connection (single PC, or router) only.