>what is the command for macro substitution in vb

Depending on what you are trying to do, you might be able to use the script control like so:

Private Sub Command1_Click()

   
   Dim oSC As ScriptControl
   Dim iVal As Integer
   Set oSC = New ScriptControl
   oSC.Language = "VBScript"

   Dim toexe As String
   toexe = "4*5"
   iVal = oSC.Eval(toexe)

   MsgBox iVal, vbOKOnly, "Value of iVal"
clean_up:
   Set oSC = Nothing
End Sub

Check out the documentation in MSDN for the scripting runtime.