Internet for 15 seconds, then nothing...

Ok, I have an Actiontec router from Verizon and a Belkin wireless G pci network card. I get between a "Good" and "Very Good" signal from about 50 feet away. However, I only get internet and am only able to log into the router for about 30 seconds, and then I get nothing. Windows says the connection is still good, though. It's weird, because the thirty seconds starts as soon as I open Firefox or IE. For example, if I start up the computer and immediately open Firefox, I have 30 seconds to browse the web, even though it never disconnects from the router. If I start up the computer, wait three hours, and then open up Firefox or IE, I still only have thirty seconds of internet connection, even though the computer is telling me it's fine. The connection is even pretty snappy during those thirty seconds.

I just did a fresh install of XP with SP2. Anyone have ideas? It's driving me crazy.

Also, I know the title says 15 seconds, but it varies a little bit.

What is the activity light doing on the router when your connection drops? Can you Ping your gateway address when the internet drops off?

The wireless activity light stays on, and no, I cannot ping the gateway. I was just trying to download a file, and it was at 79 kb/s for a few seconds before it stopped.