As an inveterate mucker about (or should that be muck abouter?), I sympathesize with those who just have to muck about with a computer. But one should really take precautions, all of which I figured out years ago, in Mac OS 7, where you could do a lot of really radical surgery.
The first principle is to always know at least three ways to boot your computer--as in a startup drive, a second bootable drive, the install disk--and try out all of them before you do anything else.
Second principle: always have a way to back out of what you did. These days a current Time Machine backup ought to work. But being a bit distrustful of new things on a mission critical function I also have a bootable clone of my current system. Actually, I also have bootable drives containing Tiger and a fairly pristine Leopard install as well. You can never have too many drives.
Third principle: when tinkering first make a copy of the file/folder you are about to tinker with, and work on the copy. Thus, if you are going to alter a system file, drag it to the Desktop, open that version and edit it. Save your edited version somewhere else (I have a Mods folder where I save such things), then replace the file in the system folder with your edited version and see what happens.... If what happens is unfortunate you can use an alternate boot method, and then put the original version back. Of course, in Leopard things get a bit more complex because of ownership and permissions issues, but it is all still "doable" if one is sufficiently determined. Basic knowledge of UNIX and the Terminal is pretty much essential. A good place to start is here:
http://www.osxfaq.com/Tutorials/LearningCenter/index.ws
And a good place to look for interesting things to do/modify is MacOSXHints:
http://www.macosxhints.com/
Mucking about without a safety net can lead to very unhappy outcomes.
Francine
Francine
Schwieder