Docking pane width

Hi, I'm using the docking pane manager on a VB6 sdi form. The form also has a command bar and window tree-view control. I am opening two panes when the form is loaded; both docked to the top of the form. My problem is that the panes are opened accross the full width of the form so that my treeview control (which runs down the left-hand side of the form) covers the left most portion of the panes. What I want is for the width of the panes to be such that they are as wide as the form less the widht of the treeview control. I've tried quite a few things but nothing seems to work. Any help would be greatly appreciated.