inner DIV locked to lower right hand corner of outer DIV

position is your friend

<div style="width: 500px; height: 150px; border: 1px solid red; position: relative">
    <div style="position: absolute; right: 0; bottom: 0; width: 200px; height: 100px; border: 1px solid green;">
    </div>
</div>

<div style="position:relative; width: 500px; height: 500px; border: 1px solid red;">
    <div style="position:absolute;right:0px;bottom:0px;width: 200px; height: 100px; border: 1px solid green;">
    </div>
</div>

Give that a try. Short version: position:relative on the outer div, position:absolute on the inner div and tell it you want the inner div to be 0 pixels from the right and bottom edges of the parent container.