Down load the new firmware and install it in your router.
http://kbserver.netgear.com/products/WGR614.asp
Use UPnP. If your router supports this. Turn it on. The router will work out the ports it needs to open for Xbox live. If your router does not have this feature, check the manufacturers website for the latest firmware. (also make sure portforwarding and/or DMZ is turned off as they interfere with UPnP)