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Mac OS X:

Command-Shift-3 => Screenshot of entire screen
Command-Shift-4 => You can Select which portion you want
Command-Shift-4, <spacebar> => You can choose a specfic window

arn
 
I was going to suggest SnapzPro X which came with my Mac. Normally, in addition to the functions above, it also takes moving screen shots - except just now I was going through the keystrokes to post them to you and it caused a complete benny and I had to restart!

Its really good, honest.
 
Originally posted by passthejonch
how do i get a jpg file of my desktop?

do the screenshot as above, then open Preview >export>choose the format and location you want to save the jpeg to
 
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