Flash game ground

Hi all. I’'ve been creating a flash game for the last couple of weeks and have most of the code sorted out. I’m now at the stage of putting in the graphics.

Can anyone help me with the ground. Basically my game is a car race. The car static and the ground scrolls from right to left under the car… currently i have the ground as a solid shape in flash, and i want to create some detail on it. what would be the best way to do this. i was thinking a jpg but that would be way to big…

Any one got any ideas or examples???

Thanks very much for any ideas at all. Even if its just a point in the right direction.