Maybe you could have the user "throw" the ball so far and if they can do it they get money to buy upgrades to the ball? Then they would go to the next level where the height needed would be higher?
I don't know, just an idea.
Thanks everyone :)
deli conker, I do realize that my tanks are not as realistic as they could be, but keep in mind that this is a flash game. Also, you probably had 2 bullets left because you had fired the other off a bit before. The machine gun doesn't reload until all of the bullets are used. :) Thanks for the advice.