Only Two Macs Are Connected Not All 4

I moved into the new house with two laptops with Windows Vista installed. Since then I have been experiencing severe problems with the wireless connection. The operator is TalkTalk.

As soon as we realised that the problem seemed to exist exclusively on our Vistas (since the two Macs, of another couple of tenants who had been living here for long, were working correctly as usual) we called the company. They suggested many things I have already read on this forum such as deleting the other networks, re-adding mine manually etc. We then realised that things were more complicated than initially thought and started analysing the problem more in depth. We went through their website and changed different settings, including those listed in the properties of "Manage wireless connection" or sth like that (we changed some IP configurations, the protocol ivp4/6, etc.). The outcome was that my Vistas started working while the Macs stopped.

I called them again many other times but no conclusive solution was ever found. I eventually talked to another operator who drew the conclusion according to which the WEP configuration of our Vistas is not compatible with that of the MAC. In other words either the Vistas would work or the Macs. No way they could both work at the same time!!!!