Control of Layers!!

Hi!
I'm using the following script to show banner inside pages out of my server:

<script language='javascript'>
var IE4=(document.all) ? 1 : 0;
var NN4=(document.layers) ? 1 : 0;
if (IE4) {
var theSource='<iframe id="Floating" src="http://www.mywebsite.com/banners.shtml" width=300 height=100></iframe>'
document.write(theSource)
} else if (NN4) {
var theSource='<layer id=Floating src="http://www.mywebsite.com/banners.shtml" width=300 height=100></layer>'
document.write(theSource)
}
</script>
But I don't know how to control the position of the Layer.

Any Ideas!

Thanks

Rui