How to have drop down menu appear in different frame.

[GVCBen]

I am working to clean up my work's website by creating a drop down menu.  This will clean up pages and make it much easier to find content.  The CSS generator has created some nice code to plug into my website.

I am wondering how I might be able to edit the code so that I can place the main menu items in my 'top_nav' frame, but have the drop down appear over whatever content is in the 'main' frame area.  I only have very basic knowledge of code etc.  Any help you can offer would be great.  Maybe what I want requires a major restructuring of the website...but I'd rather not do that!

Thanks,
Ben