you need vba for that.
if your db is not split, you need to add this on a Module
Code:
Public Function open_denywrite()
Static rs As DAO.Recordset
Dim db As DAO.Database
Set db = CurrentDb
On Error GoTo access_fail
Set rs = db.OpenRecordset("table1", dbOpenDynaset, dbDenyWrite)
Exit Function
access_fail:
MsgBox "Somebody has opened this already!"
DoCmd.Quit
End Function
create an Autoexec macro that will Run (Runcode) the above function.
"table1" there is but sample table, you may use a "dummy" table or temp table.
Access is multi-user out of the box. If you are created your application using best practice suggestions, there is no need to prevent other simultaneous users. As someone already mentioned, you DO have to split the FE/BE so that only the BE (data) is shared and each user has his own personal copy of the FE (application objects)