I learned about this at work and thought it was really cool and figured I would put it on my blog.
If you are like me, sometimes you want to take screen shots of just one window or application (instead of 3+ screens as I know some of the people have).
The normal screenshot is done using the Print Screen button on your keyboard, sometimes on laptops, etc. the button will read "Prt Scr".
When you hit this button and paste it into a graphics program, it will place a screenshot of your entire desktop(s).
Normal Print Screen takes a picture of the screen and not the application or window in focus. If you have to open a editing program and go cropping the image, it just isn't any fun.
You hold down the Alt key when you hit Print Screen or Prt Sc.
Hope this is useful and saves you time without having to get a program just for cropping or screenshots (plus there is a tool built into Vista to help with this called Snipping Tool)