Creating a Multiuser Access Application by Linking Tables

First check Tools > Options > Advanced tab for Default Open Mode = shared, Default Record Locking = Edited Record and Open Databases Using Record Level Locking is checked in Access on all computers including the sever.

Then check the security settings and share settings.
For databases on network computers, go to the level that is shared. Usually that is an entire drive. Right click on it and select "Sharing and Security". Make sure "Share this folder" is selected and there is a share name that does not have a dollar sign ($) behind it in the drop down box. (The dollar sign share is a default share for administrator only.) If there is not one, add it. Select a share without a dollar sign. Select permissions. Make sure the users that will be using the DB have change and read permissions.

Then right click on the folder(s) that contain the database(s) and select "Sharing and Security". Select security. Make sure the users have read, write, modify, and read & execute permissions. Select advanced. Edit the users that will access the databases. Make sure they have create files and delete permissions.

Then right click on the the database(s) and select "Sharing and Security". Select security. Make sure the users have read, write, modify, and read & execute permissions.

All databases are heavy network users. Running a multi user Access database, all workstations should be running the XP or Vista pro version. If you have less than about five workstations, you might get away with the backend being on a system running pro but more than that or with a complicated database, you need a domain and the server running a server OS. Get up to a dozen heavy users or a couple of dozen light users and the server should be a true server and be dedicated to only serving the one database.

Each user should have there own copy of the front end. The front end should not be shared. To simplify future updating of the front end see www.thenelson.name/#CheckForUpdatedFe.  Installing it on each user's machine allows you to place the updated front end in one special location and everyone's front end would then be automatically updated as they open the database.

Please clarify "Please clarify when specifying the share and the permissions for the folder and for the file, for both the front-end and for the back-end."  What additional information do you need?

One other sharing requirement for Vista (and A 2007):
Make sure your database is in a "Trusted Location" or no code will run. More info:
http://office.microsoft.com/en-us/access/HA102564121033.aspx

As for record locking:
One of the biggest concerns in a multiuser environment is what happens if two or more people try to change the same information at the same time.  The way that this is handled is through locking.  If you look up "lock" in Access and VBA help, you will see record locking, all record locking, page locking, optimistic locking, pessimistic locking.  99% of the time you want pessimistic record locking (editied record) or optimistic record locking (no locks).  Then the question becomes optimistic or pessimistic locking.  Access uses optimistic record locking by default in its forms.

Optimistic locking allows two or more people to edit the some data at the some time but throws an error  if they both try to save the edited data. The optimist says "It's unlikely that two people will be in the same record at the same time."  The pessimist says "Yah, right!  And most likely, it'll be my boss that's in the same record as me!!"  In our medical office, we have over 2000 patients in the database so you might think it is pretty unlikely that two people would be changing the same patient at the same time.  Until you realize that we are only seeing ten of those 2000+ on any given day.  Until I switched to pessimistic locking for the patient records, we were getting a lot of write conflicts.  I use optimistic locking for the rest of my db.

If you use optimistic locking, you can reduce the risk of write conflicts by breaking your forms up into subforms or tabs.  Records are saved when you move to a subform or another tab.  You can also put in "Me.Dirty = False" in after update events for some or all controls to save the record.

If you don't want the second person to be able to save changes to a record when someone else has not finished saving then that is called pessimistic locking.  The code below (thanks to Jim Horn if my memory serves) will notify the second person that the record is in use and by whom.  The biggest downside of pessimistic locking is the famous employee went to lunch without saving or logging off.  The computer goes to screen saver, locks and no one but the missing employee can save the record.  This can be resolved by 1: automatic logoff (of database or windows) after timed inactivity; 2: automatic save by setting the timer interval with the form's on dirty event and "Me.Dirty = False" in the timer; and/or 3: a reminder to save the record.

Function IsRecordBusy( _
    rs As Recordset, _
    Optional UserName As String, _
    Optional MachineName As String, _
    Optional CreateMsg As Boolean = True) As Boolean
      ' Accepts: a recordset and two string variables
      ' Purpose: determines if the current record in the recordset is locked,
      '          and if so who has it locked.
      ' Returns: True if current record is locked (and sets UserName
      '          and MachineName to the user with the lock).  False if the
      '          record isn't locked.
      ' From: Building Applications Chapter 12
         
          Dim ErrorString As String
          Dim MachineNameStart As Integer
         
10       On Error GoTo IsRecordBusy_Error

20        IsRecordBusy = False
40        rs.Edit                     'Try to edit the current record in the recordset.
50        rs.MoveNext
60        rs.MovePrevious
70        Exit Function               'No error, so return False.

80       On Error GoTo 0
90       Exit Function

IsRecordBusy_Error:
100       If Err = 3260 Or Err = 3197 Or Err = 3188 Then   'Record is locked -- parse error string.
110           If CreateMsg Then
120               ErrorString = Error$
130               UserName = Mid$(ErrorString, 45, InStr(45, ErrorString, "'") - 45)
140               If UserName = "" Then UserName = "(unknown)"
150               MachineNameStart = InStr(43, ErrorString, " on machine ") + 13
160               MachineName = Mid$(ErrorString, MachineNameStart, Len(ErrorString) - MachineNameStart - 1)
170               If MachineName = "" Or MachineNameStart = 0 Then MachineName = "(unknown)"
180               MsgBox "This record is being used by " & UserName & " on station " _
                      & MachineName, vbExclamation, "Record Lock Warning"
                  Err.Clear
190           End If
200       Else
210           MsgBox "Error: " & Err.Number & ", " & Err.Description & ", IsRecordBusy, " & Erl
220       End If

   On Error GoTo 0
End Function

Call the function with:
    Set rstForm = Me.RecordsetClone
    strBM = Me.Bookmark
    Set rstFormClone = rstForm.Clone()
    rstFormClone.Bookmark = strBM
    If IsRecordBusy(rstFormClone) Then
          Cancel = True
          Exit Sub
    End If