I'm trying to create an XHTML-compliant skin from a table based layout that a designer gave us.  Everything is working perfectly, but I need some help setting my column heights up so that all three columns fill to the height of the content pane without trying to add a pixel height to the 2 sidebars.  Right now, if there's long content, my menu column or sidebar column doesn't fill to accomodate the full space.  Can someone point me in the right direction?  Is there a tutorial somewhere on the site that I haven't stumbled across that will help me?

#content
{
    padding: 0;
    width: 1000px;
}  
#menu_container
{
    position:relative;
    float: left;
    width: 200px;
} 
#primarycontainer
{
margin: 0 200px;
background-color: #e5d680;
padding: 1em;

}
#secondarycontainer
{
    float: right;
    background-color: #d6b956;
    margin: 0;
    width: 200px;
padding: 1em;
}