Your file path misses the bit that says whether or not this is the User's or Root's path to the Plugins folder. On a Mac, it is important to install all plugins in the Root plugins folder and to make sure the User plugins folder is at least empty and preferably deleted.
On my machine, the path to the KT plun is Macintosh HD/Library/Application Support/Google SketchUp 7/SketchUp/Plugins/su2kt.rb there is also a su2kt folder in the same plugins folder. If you can't see a toolbar, make sure it is enabled through the View> Tool Palettes menu item.