Here's my two cents:
Believe me there are certainly others who are more qualified to answer this, but....
You both can connect to other sites at the same time? Can you jump into the router and see both PCs connected? My router, which isn't much, lets me see who's connected when I log into it and I can see the MAC addresses along with the assigned IP of every connected computer. I'm not familiar with Netgear, but I'll bet there is something like this on it.
If there's no problem then I direct you
here
I've never had any problems myself, but it seems that NAT and online gaming sometimes don't get along.
I'm sure you'll figure it out, but I hope this puts you in the right direction.