I've read in a few places that the concept of Allah existed prior to Muhammed. Was Allah one of many gods worshiped in pre-Islamic Arabia and, if so, what was his role in the pre-Islamic pantheon and why was this god elevated to a monotheistic level over all the others?
Allah may have been to the pre-Islamic pantheon what Zeus was to the Greek. We don't have much decent information on this, however, we know that Allah was the father of the goddesses Manat, al-Ilat and al-Uzza in the Meccan pantheon.
Allah was also the name used by Arabic speaking Christians. Bearing similarity to the Aramaic Alaha, the word was used to refer to the God of Abraham. The world Allah in Arabic means 'the god' as does the Aramaic word Alaha.
It would seem that in both polytheistic and monotheistic traditions, Allah represents the supreme god and creator figure.