can't open minecraft for mac 1.0.0(1.0.0) on mac os 10.3.9 machine

i purchased minecraft 1.0.0(1.0.0) and it opens fine under mac os 10.6.8, but not on a powerpc g5 under mac os 10.3.9. i get an error that says it's not complete. if this is a version artifact where 10.3.9 is too old for this version of minecraft, is there another version of minecraft that will work? or is there a way to make things work with the latest version of minecraft?