Since no one else seems to know I'll take a shot. I'm pretty sure that isn't possible, at least not without writing some Windowblinds style OS hooks that dynamically rearrange explorer windows. Your first problem is that the dialog in your example was designed to have the FS browser extend from the top of the window to the bottom, and the thumbnail section is only designed to extend from the right of the dialog to the left of the FS viewer section. So, in order to make it look like you suggest, and I don't even know if this is something that can be done, you'd have to dynamically change the constraints on the controls such that the thumbnail view extended from the far left to the far right of the dialog and the FS view only extends down to the top of the thumbnail view. This would be fairly easy to design when creating a dialog box, but modifying the OS at runtime is a completely different story. Seeing what WB is able to do leads me to think it might be possible, but it would take some mighty hairy coding to get it working... Hope this helps at least a bit..
