Targeting Frames in Flash

I have created an html documents with two frames. A left frame named leftFrame and a right frame named mainFrame. My Flash navigation menu is in the left frame and I want the pages the load up when my flash buttons are clicked to load up in the right frame name mainFrame.
My code looks like this

getURL(“about.html”, “mainFrame”);

but anytime I click the button it loads up the about.html in a new window. I using dreamweaver as my html editing tool.
Please, help as I’ve been trying this for the past two days. I have already tried a number of tutorials on the web including the on this website but still not working.

Thank you