[Dan]

Here is a picture of the 2 horizontal tile scrolling methods, as i'v understood it.

What i have left out is the complete redrawing of the tiles method.

The only thing to consider is, which one produces less jittery scrolling on the target machine.

Explanation of the bottom part, as the picture does not clearly show's it:

First you open a screen of, lets say, 656x250, and set the displaying screen to 640,250. Tile width=16. (640+16=656)

Then you copy the part of your displayed screen. Starting point is your h-scroll value to the end of the screen (the one with width of 656).
Repeat that until you reach the point when you are able to draw new tiles (at least after 15th pixel of scrolling)

Of course this it's slower method.