Your problem is that you tell XNA/SilverSprite that your "content" is located in a folder called "Content".
Content.RootDirectory = "Content";
Then you place your car.png in the root folder and try to load it like this:
car = Content.Load<Texture2D>("car");
That will throw an exception at you, as your .png isn't located where SilverSprite think it is. To make it work make a folder called "Content" and move your car.png into that one, then it works :)