With Touchstone's historical epic The Alamo now in theaters, a new DVD set promises to detail the ''true story of courage.'' Sure, it lives up to this billing, but that's not the reason the documentary about the 1836 incident is interesting. Its interviews with diehard collectors -- don't miss the Kenny Rogers look-alike talking about Davy Crockett ladies' underwear -- demonstrate how the lives of Texas trinity Crockett, Jim Bowie, and William Travis have infiltrated pop culture. The doc is especially impressive in the way it assesses the historical accuracy of the racially disturbing D.W. Griffith-supervised Martyrs of the Alamo: The Birth of Texas (1915), and even John Wayne's 1960 classic, The Alamo. EXTRAS The original trailer for Wayne's film is timeless fun; a ''Remember the Alamo'' educational film and a uniforms and weapons featurette are skippable.