umm i'm pretty sure there is ONE easy button to fix your prob m8. I have flashmx..and i think it also applies to Flash 5. When you have made a motion tween, and selected the image, under the object's properties is a button there is a rotate button, and it is selected by default as auto, to rotate the thing, you gotta change it to CW or CCW (clock wise or counter clock wise).
If you dont have flashmx it might be a bit hard to understand what i'm saying. But hopefully it will get you somewhere. Because if you find that option, it gives you a smoother result than using motion tween and doing it yourself manually.
Later