I've had the same problem myself. I have the same router and everything. What Link mentioned will only help you host games, and that's all. We have a special problem. We need to open up additional ports to be able to play JJ2 online. You can copy me and live on the wild side, although I should mention I use another firewall, BlackICE that is, for extra protection. I don't know how safe this is, but if you think it's worth it, give it a try:

Open up UDP ports 1026-1079, 1081-3127, and 3129-4999. This may not work 100% of the time, but it should work in general (at least that's true for my comp).

An alternative (aka the super lazy/risky way) would be to just temporarily enable your DMZ which will "allow a single computer on the LAN to be exposed to the Internet." In other words, this will open all ports and make your comp vulnerable to stuff. Do whatever you want, but just don't blame me if something bad happens (how nice of me to mention this). But I haven't been hacked to death as of yet, just so you know.