Need threaded pane visible while scrolling post

[arob42]

I'm looking for a mod that will keep the threaded pane visible while scrolling through a long post below it. So, ideally there are two panes in the browser, the top one is the threaded view and the bottom is the post view. The center can be adjusted higher or lower with a click and drag of the mouse (optional). Scroll bars appear for the lower pane when the post is too large to fit. The scroll bars already appear in the upper pane. Is there such a hack available?

Perhaps this is more of a skinning issue.

Thanks,
--Robert