I have the same problem running SketchyPhysics3.2 on sketchup 7 and Mac OSX 10.5.8 on Intel Core 2 Duo:

Error Loading File sketchyphysics.rb
dlopen(/Users/dr/Library/Application Support/Google SketchUp 7/SketchUp/plugins/SketchyPhysics3/sdl/SDL_Special.dylib, 9): no suitable image found. Did find:
/Users/dr/Library/Application Support/Google SketchUp 7/SketchUp/plugins/SketchyPhysics3/sdl/SDL_Special.dylib: unknown required load command 0x80000022