Groans in pain Ouch. Flash so complicated for me
I couldn't tell you for sure how to do it in Flash (mainly because I don't know Flash, although that's a pretty basic thing to do. I don't know whether it would be advisable to do in a banner (as banners tend to be...small), but you can see it in [a lot of [url=http://www.bestwebdesignaward.com/]flash websites](http://www.themar2.com/) around the web.
If I'm not mistaken, you can also achieve what you want with AJAX.