Christianity and Islam - is there a point of dialogue?

I've been reading an interesting book over Christmas, and that is Alister McGrath's recent book 'Heresy' and alongside a general discussion on the origins of heresy he has some interesting things to say about the subject of dialogue between Christianity and Islam.
There seems to be a general understanding among Christians (as it seems to me) that although Islam recognises that Abrahamic connections between the two faiths, that when it comes to the New Testament, and particularly the person of Jesus, then everything falls apart.
McGrath makes much more sense of the whole situation. He looks at the Islamic view of the Trinity, which is generally understood to be that Christians worship three persons - God, Jesus and Mary.
Where does this strange viewpoint come from?
Well, apparently it hails from a heretical viewpoint that was influential in Arabia at that time (the Collyridian sect which flourished in the Middle East.) One of its characteristics was to treat Mary as a godess.
The situation is similar in Islam's understanding of Jesus. Christian orthodoxy was slow to find its way into Arabia, and early heresies seem to have prevailed. Particularly here we must consider the Sethian Gnosticism (sorry!) which insisted that Jesus did not die on the cross, but was substituted at the last minute by Simon of Cyrene.
It seems inreasingly clear that Qur'anic interpretation of the Gospel is heavily influenced by encounters with the form of Christianity that was prevalent in Arabia at the time of Muhammad - and that these would be regarded in retrospect as heretical rather than orthodox belief.
So, with regard to conversations between these two faiths, it would seem that we have a point at which we can agree with our Moslem friends. As McGrath says 'Christians would concur in criticizing such beliefs as they are presented in the Qur'an. Muhammad may well have been correct in identifying unacceptable Christian view about Jesus and God - they were based upon views which would have been deemed as unorthodox and heretical by the Church a a whole.
That's not a critisism of Islam, but rather an appreciation that at that time, Christianity was really struggling to achieve a degree of conformity in what it believed about Jesus and the nature of the Godhead.