Is your menu really expanding across the frameset? I didn't know anything could do that.

An alternate work around in pseudo-HTML/CSS:

<div class='master_container' style='width: 100%'>
<div class='my_menu_container' style='width: 100%; height: 50px;'>
<whatever class='my_menu' style='float: left'></whatever>
</div>
<div class='content' style='width: 100%; style='float:none'>
<img />
</div>
</div>

Without knowing what type of menuing or layout your seeking the code layout is likely not at all what you're after. That is just to give you the general idea of the a framework that would allow the effect you've described.