prova così:

codice:
Private Sub WheelCatcher1_WheelRotation(Rotation As Long, X As Long, Y As Long, CtrlHwnd As Long)
Dim ActValue As Integer
Dim Increm As Integer

ActValue = VScroll1.Value
Increm = VScroll1.SmallChange * Rotation

If CtrlHwnd = Me.hWnd Then
    If ActValue - Increm < VScroll1.Min Then VScroll1.Value = VScroll1.Min: Exit Sub
    If ActValue - Increm > VScroll1.Max Then VScroll1.Value = VScroll1.Max: Exit Sub
    VScroll1.Value = ActValue - Increm
End If

End Sub
la routine si basa sul valore di SmallChange della ScrollBar, quindi puoi ottenere un incremento più o meno ampio impostando diversamente questo valore.

Boolean