Judaism, Christianity, and Islam all worship the same God, the God of Abraham. That is where the similarity begins, not ends.
Does God say it is okay to kill someone if they commit adultry? All those reading the Koran believe so. Same God? Me thinks not. Hostorically the same God? Maybe. Realistically the same God? No.
If I create a religion (David Koresh) where I get to sleep with all the female memebers of my church and I base it on the Bible, do I worship the same God as you? No, I am worshipping a false god which I have created becuase I have distorted the true meaning. Islam. Nuf said.