The code doTEST_XLS below creates a command button.  Once the button
is created, in VBA, how do I create the sub or function I want to
run?  For example, if I want to create this MsgBox, what must I add to
my  doTEST_XLS code?

Private Sub CommandButton1_Click()
   MsgBox ("Hello World!")
End Sub

This creates the comand button:

Sub doTEST_XLS()

Dim objXL As Object
Dim strWhat As String, boolXL As Boolean
Dim objActiveWkb As Object

   If fIsAppRunning("Excel") Then
       Set objXL = GetObject(, "Excel.Application")
       boolXL = False
   Else
       Set objXL = CreateObject("Excel.Application")
       boolXL = True
   End If

   objXL.Application.Workbooks.Add
   Set objActiveWkb = objXL.Application.ActiveWorkbook

   With objActiveWkb.ActiveSheet.OLEObjects.Add("Forms.CommandButton.
1")
       .Left = 35
       .Top = 200
       .Object.Caption = "Hello World"
       .Width = 100
       .Height = 50

   End With

   objActiveWkb.Close savechanges:=True

   If boolXL Then objXL.Application.Quit

   Set objActiveWkb = Nothing: Set objXL = Nothing

End Sub