Identity and Religious Pluralism: A Reply to an Email

I recently received the following email from a friend. I thought I would post my reply here. Read it below the fold.

Do you think that Muslims and Christians worship the same God (i.e. is Allah of Qur'an the same God as God of the Bible)? Obviously there are some major differences concerning how God is described in each, but do you think that means we are worshipping different Gods? What aspects of God are essential to believe in so that you are actually worshipping Him?