Con esta función seleccionaremos todo el texto de un textbox.
Public Sub TextSelected()
Dim i As Integer
Dim oMyTextBox As Object
Set oMyTextBox = Screen.ActiveControl
If TypeName(oMyTextBox) = "TextBox" Then
i = Len(oMyTextBox.Text)
oMyTextBox.SelStart = 0
oMyTextBox.SelLength = i
End If
End Sub