And if u don't want to type it every time then go to the game folder\mods\bf2
(default is C:\Program Files\EA GAMES\Battlefield 2\mods\bf2\) and open up the GameLogicInit.con file. Then on the last line type the command (renderer.drawfps 1) This way it should be turned on everytime u open up the game so u don't need to type it always.