How bottom justify a div and have all the space above it another div with scroll bar

I used http://limpid.nl/lab/css/fixed/left-sidebar-and-header to learn how to make fixed divs to simulate the old frame tags. Works great but now I have a problem.

On the sidebar on the left I am trying to add 2 divs. "checkout" is aligned with the bottom and is 250px tall. "cart" is of an unknown height but I want it to fit above checkout. Using

div#checkout {
 bottom:0;
 height:250px;
 left:0;
 width:100%;
}
dive#cart {
 top:0;
 bottom:250px;
 left:0;
 width:100%;
 overflow:auto;
}

By placing these 2 divs inside the sidebar it works in firefox but ie will place checkout and cart in the right spot but cart will have a height going off the page with no way to scroll if the div has enough lines in it.

Anyone know a way to make this work in both firefox and internet explorer?