See Captain's Blog: Form 540, the blog devoted to my gaming activities.
Last year I order two of the Warriors of Islam army pack deals from Black Tree Design Miniatures. The first was AB1059 Warriors of Islam Archers (20 figures) which I used to make five 3 Man Shooter Elements and three 2 Man Psiloi Stands. The second package, AB1058 Warriors of Islam Crossbowmen (20 figures) provided five 4 Man Shooter Elements. For either DBM or WRG Ancients the Crossbowmen represent Regular Troops and the Bowmen Irregular.
I got the idea of how to paint them by looking at the Warhammer Ancients sourcebook on El Cid.