To take a screen shot of the currently active window, press ALT+PrintScreen.
That copies the image to the clipboard. To save the image, paste it into
your handy photo editor -- Microsoft Photo Editor or Microsoft Paint will do
nicely -- and save it as a GIF or JPEG. Voila!
This depends on if you are looking at the Command prompt
in the OS or the Command Line interface (old dos mode
looking...) if you are in the OS make sure that you make
that the active window, hold the Alt key and press the
Print Screen SysRq key (above the insert key on your
keyboard). From there you should be able to paste that
into an e-mail or word processing document.