Comment added to: "Having Fun with MacRuby on Snow Leopard" http://www.icoretech.org/2009/08/having-fun-with-macruby/comment-page-1/#comment-56
Cool howto! You might want to note that now and for the forseeable future ths will only work on 64bit capable machines. There are a few machines that can install 10.6 and run it just fine, but have no support for 64 bit and cannot build current macruby (as confirmed on the mailing list in Aug), although it is planned to have 32 bit support (back) in the 0.5 release.
If anyone is in doubt, this snippet may assist, run in Terminal:
If anyone is still reading they may be interested to know that "Snow Leopard" 10.6 XCode (3.2) includes support for C, C++, ObjC, and AppleScript only. Other language bindings may work (PyObjC is reportedly okay, from svn) but no others shipped. MacRuby 0.4 install may work some. RubyCocoa is in Ruby but not XCode. Oh and they changed InterfaceBuilder again, and I have yet to figure out how to add Outlets without editing source (.h or .rb) files.