"MetaMorphX is the premiere program for themes in MacOS X. Before MetaMorphX users were, at best, required to run an installer each time they wanted to switch themes. Often users were forced to login as root and manually move the Extras.rsrc into the right place. Switching themes now is as simple as launching MetaMorphX, authenticating, selecting the theme that you would like to switch to, and logging out (And this is a problem with OS X, no way around it.) "