Since we don't know what you've already tried, forgive me if start out simple.
First, do the complete design without any Flash content. Create 3 <div>s that are positioned next to one another, 3 across the page. Use a background color or an image as a stand-in for the Flash. Work out all the CSS before you add the Flash. That will isolate problems as CSS or Flash related.
Here's a sample 2 col page that you might be able to adapt. The trick is to put one <div> inside the other to control width.
Code:
<html> 
<head> 
 
<style> 
    div#column1-wrapper { 
        width: 100%; 
		background-color:#00FFFF;
    } 
 
    div#column1-wrapper { 
		background-color:#00FF00;
    } 
 
    div#column2-wrapper {
		 background-color:#ff0000;
        float: right; 
        width: 250px; 
    } 
</style> 
</head> 
<body> 
    <div id="middle-wrapper"> 
    <div id="column1-wrapper"> 
        <div id="column2-wrapper">  <!-- Must be first --> 
            This has to be 250px wide 
        </div> 
        This has to be 100% - 250px wide 
    </div> 
</div> 
</body> 
</html>
After you get the CSS worked out, then you can move on to inserting the Flash into the <div>s.
Best wishes,
Eye for Video
www.cidigitalmedia.com