I have the exact same setup on one of my machines. The first time I encountered this problem, I fought it for hours. It's really a very simple problem, but when you're a Linux newbie, it seems like a mountain. You just don't have your gateway address in the configuration. Go back through the network configuration procedure, and make sure you got it all. If it still doesn't work, I can get you some file names where you can set it manually. That's what I had to do. The only hard part is finding the files.