The ignorance in this forum is appalling. I confess, before I started my study, I was woefully ignorant too. (Not directed towards you, Cycel, I just wanted to also comment on this)
The history of Islam is one of interpretation. There are all kinds of interpretations, that have been done since the Qur'an was supposedly dictated by Allah (NO, I do NOT believe that - it is not inspired.)
Basically, Mohammed had a Catholic wife, and learned much about Christianity from her. He also went to Jerusalem and learned about Judaism. Then he twisted things around and added his own touches. That is why the Qur'an thinks that Jesus, God the Father and Mary are the Trinity. Wrong, but coming from 6th century Catholicism. (Not saying any Catholics here believe that!)
For one thing, the Qur'an is not just about Allah, but Jesus! They believe he is the Messiah! ....................