So can you even start GW? Or does it give you the error right away when you launch the executabe?
Your routers support page is here :
http://kbserver.netgear.com/products/WGR614.asp
you should check to see if you have the most up to date version. I believe that GW should just require NAT, which pretty much all routers support. the only time you need to open ports are if people are joining YOU, not vice versa. Most recent network games come "nat aware" and know how to used established connections instead of requesting a connection to you (this requiring you to port forward).
You shouldnt need UPNP on. And if you have spent a decent amount of time messing with the router, maybe you should try restoring it to default. Write down all the major info you need off it and reset it so everything goes back to default. You shoultn have much issue after that.
For games like Warcraft 3, if you want to play a custom game and youre the host of it, you need to forward port 6112 (GW uses the same ports) to PC that is playing the game. But unless you are planning on hosting custom games, you wont need to forward ports, battle.net hosts the game and the players connect to it (similar to GW)