Flash CS4 has added a new type of tween. It may not seem like a new tween because it has the name of an older tween. I'm talking about the "motion" tween.
What was in previous versions called the motion tween is now called the "classic" tween. The motion tween in Flash CS4 is something entirely different.
The motion tween allows you to quickly animate objects without going through all the steps you had to go through with previous versions of Flash. Now you can simply create an object or import an image. Right click on the object or image and select "create motion tween". When you do this, a dialogue box pops up and tells you that you need that object to be a symbol to motion tween.
When you click "okay", your object becomes a movie clip symbol. You'll also notice that your symbol fills in the timeline the length of one second. In other words, if your frame rate is set at 24 frames per second, your object will fill 24 frames.
Now you can simply grab your symbol and move it where you will want it to end up. You can also manipulate the path of the symbol in an infinite number of ways by grabbing the points on the spline(the line with dots that appears) and moving them.
You can also curve the line. If you want to make the animation longer or shorter than one second, and you probably do, just go to the last frame in the timeline and pull to the desired end frame number.
You can also manipulate your animation further through "easing" and the motion editor.