Maybe this is already apparent to you, but you can use Arena and Houdini to setup any position relatively quickly. Of course there are the options to disable castling certain directions and to choose whose move it is.
Simple way to create diagrams

Try:
1. Go to http://chessgames.com as you suggested. Find the game you're interested in, and select the "PGN - View" option to view the PGN.
2. Copy the PGN into your clipboard.
3. Go to http://www.lutanho.net/pgn/pgn2fen.html and paste the PGN text into the top text box.
4. Click the "Convert to FEN List" button. The FEN data for each move in the game is listed in the bottom window, one move/position per line. The last character in the line indicates the move number associated with that line.
Hi there, looking for some simple advice. I want to start creating a library of chess diagrams with important strategic positions and diagrams to reinforce my study. For example, I've just started reading Modern Chess Strategy. Right now I'm looking at a position from Alekhine-Johner, 1947 and I want to quickly create a diagram of the position after Black's 43rd move. So, I find the game on chessgames.com, for example and go to that position - now, how can I create a diagram? If I had a FEN string, I could just paste it into a free resource like chessup.net and away I go. But I can't see where to get the FEN string. Anyone got a solution? The alternative is to manually create the position somewhere like chessup, but it takes so much longer...