You will want to build an Chromeless AIR app. There are a few tutorials online that will show you how to take your existing app from a windowed app to windowless/chromeless.
Code:
<systemChrome>none</systemChrome>
<transparent>true</transparent>
I don't presently have access to Flash CS4, only Flex - but it should be the same type of method to get that look - and that's added to the (project_name)-app.xml description. Sorry for not having a Flash CS4 related answer... but I have to assume it's the same.

Hope that helps.