Considering this is a Flash forum, I'll assume you want to make the background of a Flash movie - your logo - transparent.

If so, a simple way in Dreamweaver to tell the Flash movie to display without the background is: Select your Flash movie > Look on the Properties at the bottom of the screen > For Parameter put "wmode" for Value put "transparent". Click OK.

The background of your Flash movie will now be gone.

Best of luck!