if you get "wrong architecture" that means you are using a gem that was compiled for another type of cpu. why don't you go to the page I posted earlier and chose a version that fits your computer.
I also though so but when copied the Gem.pd_darwind from pd0.38-extended to pd0.39-extended I did get the wrong archiecture error. I think the 39 version was compiled slightly differenty (i doesn't use the normal preference file for example). So the problem isn't the powerPC vis. Intel (after all I can run the 0.38 version on the same computer).
thanks Oded