Can I share my Internet Connection on Windows with Two Adapters?

This is a complex question, actually, because you need to "bridge" the two LANs -- the wired LAN and the WiFi LAN -- on the machine that is connected to both networks.

To bridge LANs, you need to open the Start -> Control Panels -> Network Connections window. Select both LANs (you're connected to both, so both should appear in the window) then right-click and choose "Bridge Connections" from the menu that appears.

If that doesn't work or you get an error message when trying to bridge the networks, it might be the case that the configuration of one or both LANs is messed up, since Windows can't bridge them. I don't know how you configured them in the first place but it might be time to delete and reconfigure the connections.

There's also a possible obstacle with the Internet Connection Services (ICS). If so, then disable ICS, create the new LANs, bridge them, then re-enable ICS.

Thanks to Windows guru Margy Levine Young for her help on this thorny question. If you want more background information on bridging networks in Windows, check out this Microsoft TechNet article.