If you have upgraded to Leopard, there are some new options you have available when capturing screen shots of regions. The options are all used in conjunction with the existing screen shot command (Shift + Command + 4).

Once you hit the Shift + Command + 4 combination, you get cross-hairs and you can define an area of which to take a screen shot. Once you click the mouse to start defining the area to capture, these new keyboard options are available:

Shift - If you hold down the Shift key, the captured are will only move in one direction (horizontally or vertically) based on the first direction you move. If you let off the Shift key, the area will change normally.

Option - Usually when you are dragging the area, it moves about the point of your first click. If you hold down the Option key while dragging, it will expand/collapse the area around the center of the current selection. Let off the Option key and the sizing goes back to normal.

Space Bar - If you hold down the space bar, it will temporarily lock the image area and further mouse movements will move this area around on the screen. Let off the Space Bar and things go back to normal.

These new options are pretty nice if you take a lot of screen shots. You no longer have to make a perfect "first click" since you can now move things around.