The playlist window could never be any wider than the main window, eh?
Yep. But that's actually a good thing, as it allows skin designs where the side panels show through spaces in the main panel.
API SetWindowPos has a parameter for z-ordering flags
Yep, but Windows likes to move them around once you start clicking on them, so you have to keep enforcing the order... the fun really begins when you add other windows/dialogs into the mix