First of all NAT is based on your ports. If you have bad internet and you know this, I would suggest not doing it. Many players get mad over the fact of bad connection. NAT simply allows you to send and receive information to and from other players, making you host. So to do this you need to login to your router and port forward certain ports. I would suggest you use portforward.com, select the Netgear WGR614. I have already done this for you.
http://portforward.com/english/routers/port_forwarding/Netgear/WGR614/
Also try port forwarding these ports as well.
http://support.xbox.com/en-US/xbox-live/connecting/network-ports-used-xbox-live
Refer to portforward.com for instructions, just do the same thing you did to the other ports.
Select the game you need and follow the instructions on how to port forward the required ports. You will need your router's username and password. If you do not know the username and password for your router, I would suggest you try your wifi connection's name and password, as this sometimes works. If not, please read the next section on resetting your router.
Now resetting your router is used to change settings and revert a router to the previous state before configuration. This means passwords, wifi, and any changes to the router will be reset to the factory settings. This will NOT ruin your internet in anyway. You can also call your ISP (Internet Service Provider) which I believe is Comcast with the Netgear WGR614 router.
To reset your router, you will find a little reset button on the back of your router. This looks like a very small black indented circle. I would suggest lighting up the router to see it as it does not stick out. Take a flat screw driver and push the button. Hold it for roughly 10 to 30 seconds. The box should flash, the internet should cut off for a brief moment, but it will come back shortly. It will not give you any message confirming you have done this.
This will now mean you have reset your router to the previous settings. To login to your router, try typing in either 127.0.0.1, 192.168.0.1, or 10.0.0.1. I can not remember what it is on that specific Netgear router.
Your password has also been reset so you can not login using your old one. You can find your default password usually on the router itself. See this link below to help.
http://kb.netgear.com/app/answers/detail/a_id/1148/~/default-password-for-netgear-devices
Also I believe, I had a lot of trouble with the default username and password myself, It was Admin and the password is comcast1234. Try that if nothing else works.
I hope this helps. Good luck!