Place four PictureBoxes on the form separated by a small distance vertically and horizontally.

In the form's move event handler, see if a drag is in progress. If it is, rearrange the PictureBoxes appropriately.

If no drag is in progress, set the mouse pointer to something appropriate (up/down, left/right, or resize all arraws).

When the user clicks and drags on the form, make the form's event handlers adjust the sizes and positions of the PictureBoxes.

Private Const SPLITTER_HEIGHT = 40
Private Const SPLITTER_WIDTH = 40

' Minimum allowed sizes for any PictureBox.
Private Const MIN_HORIZONTAL = 10
Private Const MIN_VERTICAL = 10

' Drag directions.
Private Const DRAG_NONE = 0
Private Const DRAG_HORIZONTAL = 1
Private Const DRAG_VERTICAL = 2
Private Const DRAG_BOTH = 3

' The percentage occupied by the PictureBox.
Private PercentageHorizontal As Single
Private PercentageVertical As Single

' True when we are dragging the splitter.
Private DragDir As Integer

' Arrange the controls on the form.
Private Sub ArrangeControls()
Dim hgt1 As Single
Dim hgt2 As Single
Dim wid1 As Single
Dim wid2 As Single

    ' Don't bother if we're iconized.
    If WindowState = vbMinimized Then Exit Sub

    hgt1 = (ScaleHeight - SPLITTER_HEIGHT) * _
        PercentageHorizontal
    wid1 = (ScaleWidth - SPLITTER_WIDTH) * _
        PercentageVertical
    hgt2 = (ScaleHeight - SPLITTER_HEIGHT) - hgt1
    wid2 = (ScaleWidth - SPLITTER_WIDTH) - wid1
    picNW.Move 0, 0, wid1, hgt1
    picSW.Move 0, hgt1 + SPLITTER_HEIGHT, wid1, hgt2
    picNE.Move wid1 + SPLITTER_WIDTH, 0, wid2, hgt1
    picSE.Move wid1 + SPLITTER_WIDTH, hgt1 + _
        SPLITTER_HEIGHT, wid2, hgt2
End Sub

' Return drag flags indicating the area at this point.
Private Function OverDragArea(ByVal X As Single, ByVal Y As _
    Single)
Dim over As Integer

    over = DRAG_NONE
    If X > picNW.Width And X < picNE.Left _
        Then over = over Or DRAG_HORIZONTAL
    If Y > picNW.Height And Y < picSW.Top _
        Then over = over Or DRAG_VERTICAL
    OverDragArea = over
End Function

Private Sub Form_MouseDown(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    DragDir = OverDragArea(X, Y)
End Sub

Private Sub Form_MouseMove(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
Dim over As Integer

    If DragDir = DRAG_NONE Then
        ' Set the correct arrow type.
        over = OverDragArea(X, Y)
        Select Case over
            Case DRAG_HORIZONTAL
                MousePointer = vbSizeWE
            Case DRAG_VERTICAL
                MousePointer = vbSizeNS
            Case DRAG_BOTH
                MousePointer = vbSizeNWSE
        End Select
        Exit Sub
    End If

    If DragDir And DRAG_VERTICAL Then
        If Y < MIN_VERTICAL Then
            Y = MIN_VERTICAL
        ElseIf ScaleHeight - Y < MIN_VERTICAL Then
            Y = ScaleHeight - MIN_VERTICAL
        End If
        PercentageHorizontal = Y / ScaleHeight
    End If

    If DragDir And DRAG_HORIZONTAL Then
        If X < MIN_HORIZONTAL Then
            X = MIN_HORIZONTAL
        ElseIf ScaleWidth - X < MIN_HORIZONTAL Then
            X = ScaleWidth - MIN_HORIZONTAL
        End If
        PercentageVertical = X / ScaleWidth
    End If

    ArrangeControls
End Sub

Private Sub Form_MouseUp(Button As Integer, Shift As _
    Integer, X As Single, Y As Single)
    DragDir = DRAG_NONE
End Sub

Private Sub Form_Resize()
    ArrangeControls
End Sub