People are emailing me websites that attack Islam. They say they are from the Jews and that we should send this out to everyone and tell them about it. But is this a good idea to send these sites to everyone? What about the non-Muslims? Should we tell them to be careful too? What should be done? Can we visit them at all? Should we warn others?

As regards dealing with these hate sites against Islam and those like them:

Best policy we have found in dealing with them?

Don't deal with them.
Do not go to them.
Do not mention them.
Do not argue with them.
.. and whatever you do - DO NOT FORWARD THEM TO OTHERS.
Our experience with them on the internet for the last years has taught us they will not listen, they will lie and they will take people away from the true worship of Allah, even if it is only for a while with their nonsense.

There is no need to deal with them. Allah will deal with them in due time. Please do not forward to anyone else and be sure to tell everyone else the same message, insha’Allah.