Had this problem before. I guess there are some more interested in a solution.

It seems CSplitterWnd is designed to be used in document/view-based applications only.
But by overriding some virtual methods in a derived class, you can make splitter windows based on CSplitterWnd be used in dialog based application, ActiveX-Controls using MFC:

All virtual methods that call GetParentFrame() in its implementation have to be overridden.
I have done this by using existing code except
- that I replaced the call to GetParentFrame() by a call to GetParent().
- all references or pointers to CFrameWnd were changed to references or pointers to CWnd.

I derived a class CxSplitterWnd from the class CSplitterWnd and proceeded as stated above.
Then I used this class in a dialog based application in the same way as any other CWnd derived class.
For example:

class CSampleDialog : public CDialog
{
	...
	CxSplitterWnd m_wndSplitter;
	....
}

BOOL CSampleDlg::OnInitDialog()
{
...
	// TODO: Add extra initialization here
	m_wndSplitter.CreateStatic(this, 1, 2);
	m_wndSplitter.CreateView(0,0,RUNTIME_CLASS(CSampleView), CSize(50,0), NULL);
	m_wndSplitter.CreateView(0,1,RUNTIME_CLASS(CSampleView), CSize(0,0), NULL);

	CRect rect = ...;
	m_wndSplitter.MoveWindow(&rect);
	...
}

The sample attached is a dialog based application and demonstrates the use of CxSplitterWnd. It does
nothing useful.

This is the new class declaration:

// SplitWnd.h : implementation file// class CxSplitterWnd : public CSplitterWnd
{
	// Constructionpublic:
	CxSplitterWnd() {};
	virtual ~CxSplitterWnd() {};

	// Operationspublic:
	// Overrides// ClassWizard generated virtual function overrides//{{AFX_VIRTUAL(CxSplitterWnd)//}}AFX_VIRTUAL // Implementationpublic:
	// These are the methods to be overriddenvirtualvoid StartTracking(int ht);
	virtual CWnd* GetActivePane(int* pRow = NULL, int* pCol = NULL);
	virtualvoid SetActivePane( int row, int col, CWnd* pWnd = NULL );
	virtual BOOL OnCommand(WPARAM wParam, LPARAM lParam);
	virtual BOOL OnNotify( WPARAM wParam, LPARAM lParam, LRESULT* pResult );
	virtual BOOL OnWndMsg( UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult );

	// Generated message map functionsprotected:
	//{{AFX_MSG(CxSplitterWnd)// NOTE - the ClassWizard will add and remove member functions here.//}}AFX_MSG
	DECLARE_MESSAGE_MAP()
};

// SplitWnd.cpp : implementation file// #include "stdafx.h"
#include "SplitWnd.h"

#ifdef _DEBUG
#definenew DEBUG_NEW
#undef THIS_FILE
staticchar THIS_FILE[] = __FILE__;
#endif

// HitTest return values (values and spacing between values is important)// Had to adopt this because it has module scope enum HitTestValue
{
	noHit = 0,
	vSplitterBox = 1,
	hSplitterBox = 2,
	bothSplitterBox = 3, // just for keyboard
	vSplitterBar1 = 101,
	vSplitterBar15 = 115,
	hSplitterBar1 = 201,
	hSplitterBar15 = 215,
	splitterIntersection1 = 301,
	splitterIntersection225 = 525
};

/////////////////////////////////////////////////////////////////////////////// CxSplitterWnd 

BEGIN_MESSAGE_MAP(CxSplitterWnd, CSplitterWnd)
//{{AFX_MSG_MAP(CxSplitterWnd)// NOTE - the ClassWizard will add and remove mapping macros here.//}}AFX_MSG_MAP
END_MESSAGE_MAP()

CWnd* CxSplitterWnd::GetActivePane(int* pRow, int* pCol)
{
	ASSERT_VALID(this);
	CWnd* pView = GetFocus();
	// make sure the pane is a child pane of the splitterif (pView != NULL && !IsChildPane(pView, pRow, pCol))
	pView = NULL;
	return pView;
}

void CxSplitterWnd::SetActivePane( int row, int col, CWnd* pWnd)
{
	// set the focus to the pane
	CWnd* pPane = pWnd == NULL ? GetPane(row, col) : pWnd;
	pPane->SetFocus();
}

void CxSplitterWnd::StartTracking(int ht)
{
ASSERT_VALID(this);
	if (ht == noHit)
		return;
	// GetHitRect will restrict 'm_rectLimit' as appropriate
	GetInsideRect(m_rectLimit);
	if (ht >= splitterIntersection1 && ht <= splitterIntersection225)
	{
		// split two directions (two tracking rectangles)int row = (ht - splitterIntersection1) / 15;
		int col = (ht - splitterIntersection1) % 15;
		GetHitRect(row + vSplitterBar1, m_rectTracker);
		int yTrackOffset = m_ptTrackOffset.y;
		m_bTracking2 = TRUE;
		GetHitRect(col + hSplitterBar1, m_rectTracker2);
		m_ptTrackOffset.y = yTrackOffset;
	}
	elseif (ht == bothSplitterBox)
	{
		// hit on splitter boxes (for keyboard)
		GetHitRect(vSplitterBox, m_rectTracker);
		int yTrackOffset = m_ptTrackOffset.y;
		m_bTracking2 = TRUE;
		GetHitRect(hSplitterBox, m_rectTracker2);
		m_ptTrackOffset.y = yTrackOffset;
		// center it
		m_rectTracker.OffsetRect(0, m_rectLimit.Height()/2);
		m_rectTracker2.OffsetRect(m_rectLimit.Width()/2, 0);
	}
	else
	{
		// only hit one bar
		GetHitRect(ht, m_rectTracker);
	}

	// steal focus and capture
	SetCapture();
	SetFocus();
	// make sure no updates are pending
	RedrawWindow(NULL, NULL, RDW_ALLCHILDREN | RDW_UPDATENOW);
	// set tracking state and appropriate cursor
	m_bTracking = TRUE;
	OnInvertTracker(m_rectTracker);
	if (m_bTracking2)
	OnInvertTracker(m_rectTracker2);
	m_htTrack = ht;
	SetSplitCursor(ht);
}

/////////////////////////////////////////////////////////////////////////////// CSplitterWnd command routing 
BOOL CxSplitterWnd::OnCommand(WPARAM wParam, LPARAM lParam)
{
	if (CWnd::OnCommand(wParam, lParam))
	return TRUE;
	// route commands to the splitter to the parent frame windowreturn GetParent()->SendMessage(WM_COMMAND, wParam, lParam);
}

BOOL CxSplitterWnd::OnNotify( WPARAM wParam, LPARAM lParam, LRESULT* pResult )
{
	if (CWnd::OnNotify(wParam, lParam, pResult))
	return TRUE;
	// route commands to the splitter to the parent frame window
	*pResult = GetParent()->SendMessage(WM_NOTIFY, wParam, lParam);
	return TRUE;
}

BOOL CxSplitterWnd::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult)
{
	// The code line below is necessary ifusing CxSplitterWnd in a regular dll// AFX_MANAGE_STATE(AfxGetStaticModuleState()); return CWnd::OnWndMsg(message, wParam, lParam, pResult);
}