This should work on a network.

Option Explicit
Dim tFile As String
Dim hFile As Long

Sub CheckOpen()
tFile = "C:\Documents and Settings\karmela\My Documents\Book1.xls"
'use the fullname (including path)

   If IsFileOpen(tFile) Then
       MsgBox tFile & " is open"
   Else
       'replace with your code
       MsgBox tFile & " is not open"

   End If
End Sub

Function IsFileOpen(strFullPathFileName As String) As Boolean
On Error GoTo FileOpen
   hFile = FreeFile
   Open strFullPathFileName For Random Access Read Write Lock Read
Write As hFile
   IsFileOpen = False
   Close hFile
   Exit Function
FileOpen:
   IsFileOpen = True
   Close hFile
End Function

Cliff Edwards