joey stated it pretty well. Most Muslims spell it Qur'an, because that gives a better indication of how it is pronounced.
addendum 11/3/2001

The only real theological argument I have ever seen in Islam was over the status of the Qur'an as either uncreated or created. The consensus which came out is that the Qur'an is like the attributes of Allah subhannahu wa ta'ala(Glorified and Exalted be He!) and is uncreated, and has existed for all time.

The Qur'an is in Arabic. English versions are essentially commentary, and are not considered to be the Qur'an at all, but simply the explanation of the meaning according to the translator. There are seven qirâ'ât (usually translated as "variant readings") of it, with different pronunciations and manners of recitations of the text.