What version of actionscript are you going to use? You can create a library movieclip that you add dynamically, but the code for doing it is different between AS2 and AS3.
I will be using AS2.
How would the code be different had it been AS3?
For AS2, you right click the movieclip symbol in the library and select the Linkage... option. In the panel that appears you select the first option (Export for Actionscript) and another is automatically selected. Then you assign an Identifier for it in the field at the top. To add that movieclip to the stage you use the attachMovie() method... for example...
this.attachMovie("linkageIdentifier", "instanceName", this.getNextHighestDepth());
In AS3 it is somewhat similar as far as assigning an Identifier, except you assign a Class name instead, and then add a new item to the stage as a new instance of the class...
var instanceName:ClassIdentifier = new ClassIdentifier();
I should add that you can also create movieclips out of thin air with AS2 (creatEmptyMovieClip()) and AS3 (var mc:MovieClip = new MovieClip()), but they would involve drawing things dynamically as well. That's why I suggest going the library movieclip route... less complication to deal with and gives you a little more hands on with dressing up the circle.
You can create a mc on the dynamically is as2 with the