[Flash 8 AS2] AS2 help needed

Im new to AS2 and have just started learning it. The problem I am having is i don’t know what code i would need to enter in flash which would allow several different movieclips to scroll accross the screen from right to left and once they had left the stage i would want the same thing to happen again only i would want the movieclip to scroll from a random higher or lower location than the last. This would need to be continously looped. The code is for movielcips in a game which scroll from right to left.

I have no code as yet as this is the starting code i need to program the game.

Below is a n example link of the game i want to be able to create eventually(or similar)

this uses the fish scrolling from right to left and vice versa which is the code im wanting

If sum1 can help a newbie then that wud be gr8