Scale 100% but with scrolling bar

Hi all,
Pls see this link for a better example
http://www.dreamance.com/download/demo15may/main.htm

Currently, the background and the rectangle content belong to different swf. The an main.swf will load both the background.swf and index.swf (rectangle content) and the background will scale to fit the whole window.

Problem:
If the user screen resolution is too low, how can I enforce the scroll bar in internet explorer to shown so the user can still scroll around then content?

You can download the working file at http://www.dreamance.com/download/demo15may.zip

Thanks