I was looking for a simple way to take an image capture with my iSight, without using an add-on. I discovered that if I turned on iChat and clicked on my camera icon to view the video, I could then just hit Command-C to copy, and it would copy the current image as a still to the buffer. From there, I could then paste into Preview or Graphics Converter or whatever.
Mac simplicity at its finest!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040719161324765