NT 4 Workstation Explorer Pane Missing

Both “My Computer” and NT Explorer when opened/explored only show a single pane. The left pane showing drive/directory entries shows up and consumes all available window space, and there isn’t a right pane containing the subtree contents of the current left pane selection.

All attempts of using Mickey$oft’s KnowledgeBase, etc. have yielded nothing. A local MCSE has been unable to figure it out (implying it isn’t something quite obviously wrong and quickly resolved).

What Registry Hack is required to get the the right pane working?