Turn Off Discover - Ability But Allow Ethernet?

I have Windows 7 64 Bit Pro PC connected directly to the router via Ethernet.This is I will call Ethernet Connection 1.I also have a Windows XP Pro SP3 computer connected to the same router but via a wireless connection.I have both PC's connected together via an Ethernet cable. This I will call Ethernet Connection 2.It all works fine, but I only want my PC's to communicate via Ethernet connection 2.Currently, if I disconnect the Ethernet cable between the computers I can still access the files on the Windows 7 computer via the wireless connection on the Windows XP computer.I've tried to see if this is discoverable by other people using the router by installing Ubuntu on the Windows XP machine and looking at the available networks. Lo and behold, my Windows 7 machine is discoverable and accessible - albeit by a password. This is with the Ethernet cable between the computers unplugged.I have both networks on the Windows 7 machine set to public and all sharing options switched to off. Both computers have the same workgroup name. Worryingly I can still connect to the Windows 7 machine via Ubuntu wirelessly without even using the same workgroup name!All I want to do is connect the two computers via Ethernet Connection 2. I don't want any sharing information going to the router too and hence other poeple being able to see it. Ethernet Connection 1 on the Windows 7 machine is for the internet only (same as for the wireless connection on the XP machine).