'add a field to your table (I add two fields: one for the locking and one for the username)
'give it an boolean value
'If you want to show the record first check this field

Sub ShowRecord

	If rs.Fields("Locking") then 
		'show message
		MsgBox "Sorry, data in use"
	Else
		'set locking
		rs.Edit
		rs.Fields("Locking").Value = True
		rs.Update

		'show rest of record
	End If

End Sub

Don't forget to reset the locking when you stop handling the record!

Sub Reset

	'reset locking
	rs.Edit
	rs.Fields("Locking").Value = False
	rs.Update

End Sub

If you have another field which contains the username you can use that in the messages.