Warriq's article is good, but he seems to be unacquainted with much New Testament scholarship of the last twenty years. Men like Larry Hurtado ("Lord Jesus Christ") have ably shown that the Christian Scriptures are much earlier than previously claimed, and that the oral sources behind the early writings give even greater creedence to the authenticity and credibility of the Synoptic Gospels and the letters of Paul. 

Paul's letters show a heavy dependence on early Jewish Christianity (which had to have arisen, based on the literary evidence alone, within a decade or so of the Resurrection). Paul's earliest letter, Galatians, was written in 53 or 54 - a mere twenty years after the death of Jesus, when most of the eyewitnesses were still alive and well. 

Christianity, unlike Islam, stands or falls on the historical record, and so far it has stood the test quite well, thank you.

I like Ibn Warraq's article but am surprised he doesn't know that the book by Luxenberg was published English in 2007 as The Syro-Aramaic Reading of the Koran: A contribution to the decoding of the Language of the Koran and is readily available