1) Take a screenshot by hitting Printscreen on your keyboard
2) Paste it into your favourite imaging software and crop out everything you don't need, then save it as a web format: gif, jpg or png
3) Upload it to a free imagehost like Imageshack or www.photobucket.com
Little note - holding ALT (just left of the space bar on my keyboard) and pressing print screen at the same time will only copy the window you have open at the time.