Windows XP 1. Click on the Start Menuand then click Run
2. Enter %AppData% in the window that pops up
3. Doing so will open a new window and you should see the folder labeled .minecraft inside
4. Open .minecraft and you'll see the folder screenshots.
5. Open that folder up and you have your screenshots!
Windows 7 1. Click the Start Menu, type Run, then click on it.
2. Follow steps 2-5 for Windows XP
Windows 8 1. Swipe in from the right edge of your screen/touchpad and click Search.
2. Type in Run and then tap/click it.
3. Follow steps 2-5 for Windows XP