I was making a side-scrolling game not that long ago. Side-scrolling really isn't that difficult, although I can't really give specifics on how to do it because I don't know what you're writing your game in.
The way I achieved it was by taking your level image and initially setting it to screen position (0,0), and then when the player reached halfway across the screen, the image moved left off the screen (ie. x coord - 1). Same principle with the y-axis. Although, if your level's pretty big, you'd be better only drawing the area of the level that's actually inside the screen bounds.
Let me see if I can find some of my old stuff and I'll post some code.