Adding More than One Worksheet_Change Function

Heres another way of doing it.

And as you are changing cell contents via the macro you should also use Application.EnableEvents in your code to stop the macro change event being triggered when the macro changes the contents.

Private Sub Worksheet_Change(ByVal Target As Range)
   If Not Application.Intersect(Target, _
      Range("A2:A101", "D2:D50")) Is Nothing Then
   Application.EnableEvents = False
   If IsEmpty(Target) Then
      Target.Offset(0, 4).Value = ""
      Target.Offset(0, 1).Value = ""
   Else
      Target.Offset(0, 4).Value = Application.UserName
      Target.Offset(0, 1).Value = Date
      End If
   End If
   Application.EnableEvents = True
End Sub