A useful tool built into the Mac OS, even way back in the old OS 7 days, is the screen capture tool. If you hold down the shift and command key then press 3, the Mac makes a sound like a camera clicking and a picture file will appear on the desktop.
In older Mac OSes, this was a PICT file but in OS X it's a PNG file (ping is similar to jpeg). Being able to capture what is currently on your screen is an important feature. It allows you to save things like error messages but more importantly allows you to document a procedure to be used in teaching or creating instruction manuals.
OS X takes this simple screen shot a little further. In OS X if you use the 4 key instead of 3 you can capture just a portion of the screen instead of everything. When you hit Shift-Command-4 the arrow cursor will turn into a crosshair. Just position this crosshair in the upper left corner of the area you want to capture and hold the mouse button down while dragging open a box. When you have the box over the area you want captured let go of the mouse button and that area will be saved as a PNG file.
Leopard, Apple's latest version of the Mac operating system, has gone even further. By adding another key you get even more control over the area you want to capture. Hit Shift-Command-4 to get the cursor and then drag out the selection box. If you hold the Shift key while this box is active, you can lock in one dimension. If you hold the Shift key and then move down, the box cannot get any wider. If you hit the Shift key and move right, the box cannot get any taller.
Another added action key is the Option key. Hit Shift-Command-4 to get the capture cursor. If you hold down the Option key, the box will grow out from the center instead of the upper left corner. Lastly, if you hold down the Spacebar you can then drag the box to a different location on the screen. With the Spacebar down, the box cannot be resized it can only be repositioned.
As powerful as the screen capture function is in OS X, there are other alternatives. One of the most popular screen capture utilities is SnapzPro X from Ambrosia Software. This utility is not the cheapest one out there, it goes for $69, but it is very powerful. Along with amazing 'screen shooting' abilities, SnapzPro has the ability to record a video of anything happening on the screen. Just think of the teaching aspect of this function. Instead of writing pages and pages of text with pictures on how to do something on a Mac, SnapzPro allows you to make a video of you actually doing it. This has become a popular way to do tutorials online called Screencasts (you know, like a Podcast). SnapzPro will run on any Mac that has OS X 10.3.9 or better. It's available directly from Ambrosia Software. (www.ambrosiasw.com)
For those who need to do more professional screen recordings there is the new ScreenFlow from Vara Software. This is THE software to use if you want to do video tutorials or screencasts. ScreenFlow adds plenty to this mix. First it has a built in editor. This allows you to capture at will and then edit out any mistakes or just to tighten things up. You can even add extra touches to the captured video. You can zoom in on areas of interest, add callouts, or add titles.
There are different ways to highlight what you are doing while recording a session in ScreenFlow. The mouse pointer is usually of main interest in working a computer. ScreenFlow allows you to automatically highlight the mouse, visually and/or audibly, and even have a popup with keystroke information. ScreenFlow can even capture you working on Windows software, if you have Parallels or Fusion virtualization software. This capability allows you to record both a Mac and a Windows version of the same tutorial on one computer.
ScreenFlow is only available for OS X 10.5 Leopard and is $99. You will need a newer Mac to get the most out of this program. Requirements include a G4, G5, or any Intel processor and a Quartz Extreme capable video card with at least 16MB of VRAM. I would highly recommend a Dual G5 or Intel based Mac with at least 1GB of RAM.
Whether you just want to capture a single window or the whole screen, the right tools are out there. The built-in screen capture in OS X should suffice for most users. For those who need more control, especially those who want to record their screen to a video file, take a look at SnapzPro or ScreenFlow. SnapzPro is the 'old pro' that will work on most any Mac, while ScreenFlow is the 'top of the line' that needs a top of the line Mac.