Is it ok to close the workbook whenever it's opened in readonly mode?

If yes, you could add something like this to your workbooks
auto_open/workbook_open code:

Option Explicit
Sub auto_open()
With ThisWorkbook
If .ReadOnly Then
MsgBox "Can't open in readonly mode!"
.Close savechanges:=False
End If
End With
End Sub

But the user has to have macros enabled for this to work.

=====
Alternatively, you could password protect that workbook--so no one can open it
directly.

Then give the users a second workbook to open the real workbook. That "helper"
workbook can check to see if the real workbook is already open.

Option Explicit
Sub auto_open()

Dim RealWkbkName As String
Dim RealWkbkPswd As String

RealWkbkName = "c:\my documents\excel\book1.xls"
RealWkbkPswd = "hi"

' Test to see if the file is open.
If IsFileOpen(RealWkbkName) Then
MsgBox "File already in use!" & vbLf & "Please try later."

Else
Workbooks.Open filename:=RealWkbkName, Password:=RealWkbkPswd
End If
ThisWorkbook.Close savechanges:=False
End Sub

' This function checks to see if a file is open or not. If the file is
' already open, it returns True. If the file is not open, it returns
' False. Otherwise, a run-time error will occur because there is
' some other problem accessing the file.

Function IsFileOpen(filename As String)
Dim filenum As Integer, errnum As Integer

On Error Resume Next ' Turn error checking off.
filenum = FreeFile() ' Get a free file number.
' Attempt to open the file and lock it.
Open filename For Input Lock Read As #filenum
Close filenum ' Close the file.
errnum = Err ' Save the error number that occurred.
On Error GoTo 0 ' Turn error checking back on.

' Check to see which error occurred.
Select Case errnum

' No error occurred.
' File is NOT already open by another user.
Case 0
IsFileOpen = False

' Error number for "Permission Denied."
' File is already opened by another user.
Case 70
IsFileOpen = True

' Another error occurred.
Case Else
Error errnum
End Select
End Function

The IsFileOpen function is stolen from:
http://support.microsoft.com?kbid=138621

And be sure to protect the VBA project for this helper workbook--or someone may
see the password.

Inside the VBE with your project selected:
tools|VBAProject Properties|Protection tab.

Remember all your passwords!

If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm
k-ham wrote:

Excell 2000 - I have a worksheet that performs certain functions and then
saves the file when the workbook is opened. Can I restrict opening this
workbook which is on a shared drive to one user at a time. I do not need a
"read-only" option because the second person opening the workbook in "read
only" would encounter an error due to the automatic saving of the file.

--

Dave Peterson