I do not have CS4, but from what I have heard, that functionality was removed in CS4, meaning you cannot make Flash buttons in Dreamweaver anymore. You would have to go back to CS3 to be able to do this.
Adobe removed Flash Buttons from DW CS4 for web accessibility reasons. Flash navigation is not web friendly. Try using CSS styled text links or the built-in CS4 Spry navigation tools.
FREE CSS menus.
List-O-Rama (DW Extension)
CSS Express Drop-Down Menus (tutorial)
CSS Tab Designer creates 60+ CSS Styled Button and Tab Menus (download)
CSS Menu Maker (On-Line Menu Generator)
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