I am having trouble playing on Battle.net while I am connected to my WRT300N V.1 (V1.03.06 Firmware) router. I opened the proper ports to play (4000&6112) but I still get a constant "Connecting to fastest server" message. I am sure the router is the problem because I can play Diablo 2 just fine when I connect directly to my Comcast modem. If anyone has any idea what other settings I need to change or ports to open, PM me!

Did you remove your firewall?

Yes i did

If you go into Network Connections in Control Panel, and select the WUSB300N and an unused Ethernet Adapter, you can right-click on the WUSB300N, and choose "Bridge connections".

You can also try changing the wireless mode on the WRT300N router to A, B, or G, or disable Secure Easy Setup. Some router configurations also have a "Wide" option instead of Auto.