Need Help Please In restricting access to users in Access 2010

I have created a DB which has tables,queries, forms, macros & reports and i want to restrict access to read only for the users as the DB will be placed in data share . Please advise how do i do it in Access 2010.

Alan,

i am getting a compile error stating sub or function not defined. Please advise.

Private Sub Form_Load()

Dim sPermit As String
Dim iAccess As Integer
Dim Ctl As Access.Control
Me.txtUser = Environ("username")
If IsNothing(Me.txtUser) Then
sPermit = "ReadOnly"
Else
sPermit = GetPermission(Me.txtUser)
End If
Select Case sPermit
Case "Edit"
iAccess = 2
Case "Admin"
iAccess = 3
Case Else
iAccess = 1
End Select
Me.txtLevel = iAccess
End Sub

Adding to the below, i have multiple tables,forms, queries, reports & macro. Can i give read only access for everything using the code once or do i need to use it multiple times.

Private Sub Form_Load() is highlighted and it stops at IsNothing in the code.