Its a long time ago but sharing 2 PC's with one Internet connection started for me with a "cross-over" LAN cable connected to both machines. That was before my place was WiFI-ified and more machines came into our lives at home
. I think I would still try this old method (Not knowing if it still works that way though, as I said, its a long time ago). Maybe it can become worth of looking at this rather simple solution.