use print screen key.
press the prntscr or CTRL+prntscr, the screenshot goes to your PAM automatically. U should goto MS Paint,MS word or any other graphic editors and Press CTRL+V immediately, then save the image…
if u wanna capture anything on the screen, perhaps this key can't help u. Im using PCHand Screen Capture, it could help u capture any screenshot on the screen. it offers many different capture modes inculding a scrolling window. u can get a long website page directly with PCHand Screen Capture. i think it is pretty good, i know it from my friend, u can also try it. Hope it could help.
http://www.screen-capture-record.com/