Floating Layer modified

Hello,

Ok I have done searching for this but had no luck with this particular type.

I am looking to a floating menu (which I hav found several), but…

I have a navigation on the left which goes down about 500 pixels. I need the floating layer to stay below that. Then when you scroll down past the left side navigation, the layer will begin scrolling and attach to the top of the screen and float along as the page is scrolled.

Is this possible? The thing I want to sit in the floating layer is 200w 400h. That is why i need it to attach to the top of the page, otherwise the page will scroll down forever, as it is doing now.

Any help with apprecaited.