Microsoft has made taking screen shots easier with Windows Vista with its "Snip" tool. To access it, click the Windows icon then type "snip" and press the enter key. If it's your first time using it, it'll ask you whether you want to load a Snip shortcut into the quick launch bar.
When the Snip tool has been opened you have a few image capturing options. You can grab the standard "Full screen" or active "Window" shots, along with the ability to do a "Rectangular" or "Free form" snip. The full screen and window snips are self explanatory, the rectangular option allows you to capture more than a single window up to a full screen if you wanted. The free form option is handy for capturing windows which do not have a standard shape.
The fun doesn't end after you've taken your screen shot. You now have the option to write with the "Pen" tool on the image as well as use the "Highlighter" tool to highlight specific sections. Should you make a mistake, simply use the "Eraser option. After you're done you can save it as a PNG, GIF, JPG or MHT (Single file HTML) formats or mail it off.
Screen shots made easy, definitely a worth while upgrade over the old "Print Screen" method.