I didn't use this to beat the Mario game, but I found an interesting glitch:

If you don't care about time and just want to get to level 8, then find the level where there is a green mushroom (I think it's 3 or 4) and get the mushroom. You now get 1 additional life. Then, go to the end of the level (make sure you don't have all the mushrooms) and then jump onto the green pipe and press the Down Arrow. All the mushrooms (including the extra life one) are now respawned, and you are at the start of the level, but you still have your extra life. Go and get the green mushroom, and then do the same thing over again. You shouldn't need more than 6 even if you are horrible.