A Good Start
This could be really good; keep working on it. In fact, please fix that horrible, horrible, horrible control. With what you already have done, it should be easy to implement turning while driving.
Brian's Quick Flash Vehicle Implementation Tip/Tutorial:
If and when you do implement turning while driving, take care that your vehicle turns in the proper direction when driving in reverse. It is common for Flash game developers to simply rotate a vehicle right or left--depending upon which direction the player is pressing, of course--regardless of whether the vehicle is driving forward or backward, but this is a mistake when simulating the controls of a real vehicle (i.e. pressing right or left affects the vehicle as would turning the wheel in the same direction). The vehicle should always turn in relation to the driver, so you should rotate in the opposite direction of the key press when traveling backward.
You can check out my tank demo to see how I did it:
http://www.newgrounds.com/portal/view/150998
I have been meaning to add scrolling for a while, but I do not currently have any decent multi-screen background art. I think you just gave me some motivation to get moving on that, though, so thank you. :)