How can a split view be implemented?

[Plug-In Factory]

In the media library window is it possible to define a smart view of type “Artist/album view”.
The view shows three lists that are separated with a border. The border can be dragged to resize the list. Dose anybody know how this borders are implemented. Dose WINAMP itself support that behavior or is it using the MFC splitter class? Maybe none of this is true and the WINAMP developers have written its own code that has no interface in the SDK.

Thanks for any help

Thomas