This question is a complicated one and the answer really depends a lot on what exactly you are driving at.
If you go back to Abraham and his son Ishmael that he had with Hagar, who is believed to be the forefather of the Arabs, and accept that they held on to their beliefs in the One God, you could well argue that Allah is just another name for the God of Abraham, Yahweh.
But, if you are trying to liken Muslims and Christians to each other, it becomes a whole new issue altogether, because of our Lord Jesus Christ, as was already mentioned in the thread. Whether Allah is the same as God the Father within the Trinity is not of substance in the argument of salvation. Even if he were, the Muslims do not accept Jesus as the Messiah, and that puts them on the very same level as the Jews, celebrating the God of the Old Testament, but refusing to accept the message of the New Testament.