hey there,
the easiest way to make vid caps on macs is to use the screen shot function.
1) play the video as normal. When you get to the scene you want to capture, pause it.
2) Hit the keys: cmd(apple)+shift+4
3) your cursor will change into cross hairs
4) click the cursor in the upper left corner of the frame, then drag to the lower right corner
5) release the mouse, and a .pdf of what you just took a snapshot of will appear on your desktop
6) use a utility like quick image (
http://www.macupdate.com/info.php/id/11532) to convert the .pdf into .jpg
i use the method above to make my vid caps, and it works quite well.
hugs,
marie