Scrolling Map....

I am making a platformer game and have the emgine complete, except for one thing... I can't figure out how to do the scrolling engine. I know the theory behind it, adding the tiles just before they reach the screen, but I have no idea how to implement it. Any help would be greatly appreciated.

there is a game with source code available at flashaddict.com, it's called "star guns" or something like that. just look in the tutorials->gaming section and it will be there.
i hope that helps!
jeremy