This is one of the most useful tool which is present only in windows VISTA (and also windows xp tablet PC edition). it eliminates Print screen functionality of Windows. This is probably the best screen capturing freeware available. Everytime I go back to XP I miss this tool badly. snipping tool is available for Windowx XP tablet pc edition only (other than VISTA) and can be installed with experience pack for Windows XP tablet PC edition.
It allows you to capture only the portion you want in your screen as you can see in the below picture the screen will be made frosty and the only the clear area (which will be selected by snipping tool) will be snipped and it can be saved as a image file. But to do the same process using print screen you will need to do a print screen and then edit in microsoft Paint or Photoshop.