For anyone interested in running Ruby/SDL on Mac OS X, I have a walk-through up on my blog:
http://inquirylabs.com/blog/?p=21
Ruby/SDL is a binding for the Simple DirectMedia Layer, which is a library that makes 2D (and some 3D) graphics as well as sound and basic keyboard/mouse support available in a cross-platform way. Perfect for building games with!
It was quite an adventure! Since I had such a tough time finding documentation for the procedure, I'm assuming it hasn't been done very often before. Enjoy!
Duane Johnson
(canadaduane)