Apple has included a free tool (mainly for developers) called ResEdit for years that allows you to do the same thing.
Change Menus, change or add keyboard shorcuts, change splash screens, Change the default icons for everything, lock files, make them invisible, almost anything you can think of.
You can really fuck your system if you're not careful. Unfortunately, OS X does not have an equivalent yet.
There is a great site for RedEdit users called
ResExcellenceThe site is run on a Linux box and they have a Linux section too.
[ June 27, 2002: Message edited by: cocoamix ]