That is quite easy if you know how to do it. In your CChildFrame::OnCreateClient you do:
CSplitterWnd first;
CSplitterWnd secondleft;
CSplitterWnd secondright;
first.CreateStatic(this, 1, 2); //makes panes, one left and one right
secondleft.CreateStatic(&first, 2, 1, WS_CHILD|WS_VISIBLE|WS_BORDER, first.IdFromRowCol(0,0)); //split left pane in one upper and one lower pane
secondright.CreateStatic(&first, 2, 1, WS_CHILD|WS_VISIBLE|WS_BORDER, first.IdFromRowCol(0,1)); //split right pane in one upper and one lower pane
secondleft.createView(0,0,...); //put views (or other CWnds like Toolbars)
secondleft.createView(1,0,...); //in each of the panes
secondleft.createView(0,0,...);
secondleft.createView(1,0,...);
Hope this has helped a little