Now that I have your attention, I point you to Colin Smith’s first post at Alpha and Omega Ministries introducing the Koran. The last series over there, on Textual Criticism, was quite well done. Let’s see if this one meets that standard.
Oh, and the reason for the post title is simply this: One of the most important things Christians can understand about Islam is exactly what my title says. The Koran is believed sent down from Heaven, in perfect form. Thus it equates much more to the Christian view of Jesus Himself for Muslims, than the Bible. The Bible might be more analogous to the Hadith, the Traditions in Islam.
So if you want to say something about the Koran to a Muslim, try using “Jesus” in place of “Koran” and see how offended you feel by the statement before you make it.
Here is a list of e-books on Islam available on the Internet that I compiled a while back.