If IsWkbOpened("Book1.xls") Then
MsgBox "Target workbook has been opened"
MsgBox "Target workbook has NOT been opened"
Function IsWkbOpened(sWkbName As String) As Boolean
'returns True if the target workbook has been opened
'returns False if the target workbook has NOT been opened
Dim i As Long
For i = Workbooks.Count To 1 Step -1
If Workbooks(i).Name = sWkbName Then
If i = 0 Then 'if the wkb did not found
IsWkbOpened = False
IsWkbOpened = True