Complete the fire level and get killed on the water level. Now on the high score table, enter "BBBB" for your name. This will give you infinite continues.
Run through the game as normal until you get to the level selection page. Now type in "GO PLANET". Now, when the game starts hit 'F10' and 'RETURN' together, and you should be taken back to the level selection page, where you can choose any level.