Layer positioning

I am trying to design a webpage where all the content is contained within a single 'top-level' Layer. Other elements of the page are contained within other Layers that are nested within this 'top-level' Layer.
My problem is that I want a footer (contained in its very own layer) which I need to be positioned relative to the bottom of the 'top-level' Layer (so the bottom edge of the footer layer is coincident with the bottom edge of the 'top-level' layer) - so when I change the height of the top-level layer (to give longer webpage) the footer level stays at the bottom of the page.
Hope everyone understood that!
I've tried, but I can't quite pull if off. Could someone please let me have the CSS definition for the footer layer in this case, puleeze?

You should be able to add this to your footer css:
#footer {
clear: both;
}

If that doesn't work, add a new <div class="clear"></div> right above the footer div. Your css would be the same as above
.clear {
clear: both;
}

Yeah, if clear doesn't work, post a link up to your page so we can have a looksy. Lchad's advice will work if you're using floats to acheive the columns. If you're using positioning for the columns it'll be a different story.