Allah is the god of Islam - not the God of the Bible. This god had no son, no holy spirit. "Allah" spoke to Mohammad through a trance - his words recorded in the Qur'an. Based on Allah's words in the Qur'an, he is the polar opposite of the God of the Bible. For further insight into spiritual differences between Allah and God, please refer to the book The Islamic Anti-Christ and Christianity and Islam: Differences Simplified. For more on the character of Allah, see Mohammad.
Here are several web sites that further describe the "Allah" of Islam: