Its unfortunate that very few first hand or contemporary accounts of the Arab conquests were passed down. So much of the information comes from centuries later. I would be very interested to see what tactics were used. While there are some fragments, the lack of contemporary pieces as well as the fact that little archelogical work has been done due to the troubled state of the Middle East in general means that that period is somewhat cloudy.

I too find it amazing that bands of 5,000 warriors could conquer all of Syria, Palestine, Iraq, Egypt and such. Even with exhausted Sassanid and Byzantine foes, its quite a bit of territory. Helps that neither of those empires were very religiously tolerant I suppose.