Not a great deal of point in talking to someone who is absolutely positively convinced their opinion is the truth, the whole truth and nothing but the truth. But I’ll make one last try.
It’s really difficult to research the subject because the interwebs are overrun with Christians loudly proclaiming your POV and Muslims as loudly refuting it. The websites of both sides are in general, shall we say, less than scholarly in their presentations.
So I finally ran across a post by Daniel Pipes, widely considered an Islamaphobe and definitely not an apologist for Islam or Islamism. He agrees that the word Allah is simply the Arabic word for God, equating to God, Dieu, Dios, Gott, Theos and Elohim.
You can of course continue to believe otherwise, but your opinion is not based on good scholarship.
http://www.freerepublic.com/perl/post?id=3228274,103
You have an at first glance a decent point in that the word Allah was probably used to refer to one or more pagan gods before Mohammed. The problem is that the same is true of the word for God in every other language, including Hebrew, Greek and English.
In fact, the Bible text where God commands the Israelites to not worship other gods uses the same word to refer to the other gods and to God himself.
http://biblehub.com/interlinear/exodus/20.htm
I realize you’ve been taught this and believe it, but you might want to consider the possibility that those who taught it to you were mistaken.