In theory, your program should have two states: Menu and Play.

Have a global var "State".

When in state Menu: Display 2 Buttons.When clicked, save in a Var how many players. Then Change to State Play.

When in state Play: Play.

At the beginning, you are in State Menu. It's full screen, headline, bit text, 2 buttons. When clicked, clear screen, new screen, play. Check which state you have in draw().

For buttons see: http://www.openprocessing.org/visuals/?visualID=29501

Read an example with more states here: http://mobile.processing.org/learning/example.php?name=tictactoe

Greetings, Chrisir