Viewing sprites from NES games

[FS]

I need to get a lot of character sprites from a game from which they're not easy to get through screenshots.

As I understand it, the sprites are in the game, all chopped up into pieces and organized on spritesheets. I don't need to know how to alter them or even really extract them - I just need to know how to get them on screen, so I can get them with Print Screen.

Can someone plainly explain to me how this is done, and with what emulator it's done best? I have NESten.