My game is top-down. Is there a way to have my character on the back of a truck, being driven by his friend?
There are several ways, as a matter of fact. What exactly is your problem?
The thread's title suggests it's about having the background scroll- that's no problem at all, all you need to do it set up a truck as a view, make it the player character, and scrolling is automatically handled by AGS.
Also, there are animated backgrounds (up to 5 frames I believe). You can then make objects (trees, other cars, etc) pass by using the Object.Move call and looping them once offscreen.
[Edit]: Assuming this is for a cutscene or something...
~Trent