[ecchi]

Unlike MPGs, flash movies are script driven, not just "bits of film". To do clever things like playing an advert at the beginning then stopping the film until the customer clicks you have to rewrite the script that makes the film happen. If you are serious about doing this sort of thing, I suggest you learn how to edit flash scripts. However you can get flash editors/writers that are supposed to be as easy to use as WYSIWYG HTML editors, but my experience is that they are difficult to use (but my experience is limited to only trying one of these, then giving up after spending a weekend struggling with it). Also, remember that scripts are powerful, but if you use an editor the person who wrote the software has to have added the function to do what you want, not everyone will have thought of adding as clickable advert at the beginning of the movie, so before you pay for software make sure it can do what you want.

If you just want to do this one job, and you don't think it is worth spending the time to learn how to write the scripts yourself, you may find it cheaper to simply pay someone to write this script for you.