Import a graphic you want to use by selecting File then Import to Stage. I used a plane I got from Microsoft Clipart. Place your plane on either side of the stage depending on the way the graphic is facing. The plane I am using is headed to the left so I placed the plane off the stage to the right.
Convert the graphic to a symbol by selecting the graphic and then clicking the Modify on the standard toolbar and select Convert to Symbol. Name it 'plane' and select Movie Clip as Type.
Insert a guide layer by right-clicking the topmost layer and select Add Classic Motion Guide.
On Layer 1 (plane layer) insert a Keyframe in frame 50 by right clicking and selecting Insert a Keyframe. In frame 50 place your graphic on the opposite side of the stage.
Click anywhere between frame 1 and 50 of Layer 1, the plane layer, then right click and select Create Classic Tween.
Click in frame 1 of the Guide layer and draw any path using the pencil tool 
in the guide layer. This will be the line the graphic will follow as it crosses the stage.
Add a Keyframe to frame 50 in your guide layer following the directions above to copy the pencil guide across 50 frames.
Now create Motion tween by selecting the object in the 1st frame and snapping its registration point to one end of the path. Snap the object in the last frame to the other end of the path in the guide layer.
Click Here to Show Me How to Do It!!
