Well, there is a widely-known popular hack, made by coolboyman in the Hack Section here at PC, that is also called Pokemon Brown. I suggest you change the name or it may become confused for the hack.
EDIT- To answer your question, go into a test play. Then when you're at a particular place in the game that you want a screenshot of, click the button on your keypad, Print Screen/ Sys Rq. It's located on the first row of buttons all the way to the right. Then go into Paint and Paste. Then save it and present it to us here.