Multiple networks

My friend and I have our computers here in my home. He brought a router, so we have our computers networked just fine to each other; file sharing is working without a hitch.

My computer is connected to a wireless network in my home, via a network card and a wireless AP downstairs. So, whenever I have both my wireless connection and my ethernet connections enabled at the same time, I can see my friend's pc but I have no internet connection. I only have a net connection when I have only the wireless enabled.

Is there a way to bridge the two connections together that I'm not doing? I attempted Windows bridging (highlighting the two connections, right clicking, "bridge connections") but it yields the same result as before, when both connections are just simply enabled.

The router my friend brought happens to be wireless. Is there some kind of ad-hoc'ing that I could try to connect the two routers?

Ideally, we would like to both share the internet connection from downstairs and have full sharing between the two of us.

Any thoughts?