Basically, you create a keyframe on say frame 20. On the first frame, you position your symbol as you want it to appear at the beginning of the motion. On frame 20, you modify the symbol as you want it to appear at the end of the motion. At any frame in between, you right-click and add a motion tween.
If you're still having difficulty, please read
this tutorial. It explains motion tweening very well! :)
As for having all your friends and comments in it's own file, yes, you can do that but it depends on how you want it to look. By scrollbar do you mean having your friends list scroll, as in moving from one side to the other?
(Sorry if I cannot help at some point; I'm a newb at Flash myself.)