i don't know how to use photoshop, so i just made one in paint. either take a really big picture and crop it to approximately the right dimensions (800 x 100 pixels - but fanpop will automatically resize it if it's too large), or paste a bunch of smaller pictures together so that it fits the right shape.
this is what i did for the Defying Gravity club that i created (you can check it out if you'd like) but i don't know how to just create a regular banner that you don't upload directly. good luck! hope this helps a little. :)
