have the two of the same images next to each other, the one on the bottom is flipped (like that it looks continious), then have them scroll and when the second image completes across the screen, just reset the coordinates. PM me for more info.
Whatever you're tracking for movement will keep the stored movement. I believe with BitBlt it uses a RECT structure.
I would wrap the BitBlt function up, so you don't have to call it explicitly every time. You would then bitblt the image based on this.
I would separate the space into two parts, if the position is 0, then part 1 would be the whole image and part 2 would be nothing. As you move the position, part 1 and part 2 grow and shrink depending. You would then bitblt parts of the image into each of these parts.
It's rather difficult to explain, since it's purely visual.
imagine this is the screen:
[******|***] ^ ^ 1 2
As you move the |, the pieces grow and shrink.You then make sure you draw the pieces of the image accordingly.
Are you talking for a game like super mario, or a background with scroll bars.