Helo guys, does anyone know how to make a banner expand on to html site?

Expl: There is a flash banner 500 x 60 on top of a html site, when you rollover your mouse on the banner it expands over the site to (for example) 500 x 500...

I'm looking for a solution, turtorial... I know that it can be done using javascript, but I cant find a script for it. Please help me.

Thank You