Or you could just plug the broadband into the router, and plug both computers and the Xbox into it as well...

But... it seems you're hinting is that all you have is a hub, and that wouldn't resolve the ip issues. However, I don't think the way you're wanting to do it would fix those either.

I'm going to say, in my non-network-expert opinion, that you're going to need a router.

Anybody want to enlighten me?

What is it they say about silence being golden?