The support offered here is merely to give some help to people burdoned with using Mac OS. I prefer using RISC OS based products, so I hope these documents will suffice.
Fairly sparse so far, but please feel free to ask me more.
There is a current list of possible issues at MacFixit.
Either enter sudo passwd root from a terminal window, or use NetInfo Manager in Applications/Utilities.
On Mac OS X you can simply use the Grab application, which is supplied with Mac OS X - in the Application/Utilities directory.
Under Mac OS 8 to 9.2 you can press COMMAND-SHIFT-4 which will turn the mouse pointer into a small cross-haired cursor. You can now drag a window around the area of the screen you wish to snapshot. This will be saved on the current drive as a .PICT file.
Before you start dragging, pressing the Caps Lock key will toggle the cursor between a cross-hair and a bullseye. When it's a bullseye you can click inside a window to automatically screengrab the window itself - which is handy if you don't want to worry about cropping images of windows.
If you want to grab the entire screen, press COMMAND-SHIFT-3 (which works under Mac OS prior to 8)
The snapshot will be called 'Picture 1' and each subsequent snapshot will have an incremental filename.
N.B. Holding the CTRL key down whilst carrying out any of the above actions will copy the image to the clipboard instead of saving it to disc.
I have a separate page on iPhoto Hints & Tips.