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You could have grouped these two togeather, its command shift 3 for the whole screen, command shift 4 for a crosshair to select a portion of the screen, and if you would like you can click command shirf 4 and the the space bar to get a camera which will just get a picture of the window you select.
 
PDF?

Is there a way to change the save format so that the capture saves as a jpg or something else not a PDF? Acrobat is very slow to open on my Ibook
 
Which OS are you running? It should open (pretty quickly) in Preview in OS X unless you've changed the default.... And, once in Preview, you can export it as JPEG. And, AFAIK, it just saves it by default - and unchangeably - as PDF for some (dumb?) reason from the screen capture.
 
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