Dynamic Scrolling background

Panning background in flyer game
Hey there!
Im making a game in which you fly around in a spaceship and try to avoid som evil monsters, i have it to the spaceship you fly is always centered and the enemies move towards it , and when you move the spaceship the dots current position is subtracted from the speed and new distance to the ship.
Basically the ships always centred but if you move it gives a feeling of you moving away from dots.
But to complete this feeling i want to make a background that always moves in the opposite direction of the spaceship, so if the space ship is going straight up the background is scrolling down…
Now comes my Question…
How do i make it so i have a background that is infitly long, you can always go in one direction forever , the same background is just moved and duplicated at the end of the other…
ex of what i mean:
(explanation under image)

image is located here http://xev.mine.nu/images/screen.jpg
the top image is the one in the starting position and when the user moves left the whole thing is moved to the right and when the image that is on its way in is about 50% in another is duplicated to the left of it , and then the images outside on the right are removed when they leave the area
( or about 50% outside of the visible area)
the white box in the center represents the visible area, the stuff with grey in it represents out of view area,
all boxes contain the same image

Hope someone has some time to help me out because im really not sufficient of a programmer to do all this by myself

the only thing i want to need to tell the background is the speed of horizontal and vertical movement

thank you
CJ aka VoS