Hi again,
You can add a read-only view to your InfoPath form and add a rule on load that switches to this view if a form's field is equal to a certain value (for example, if Status = "Submitted"). You can also switch to this view before you email the form so that they don't get something in the Outlook email view. You'll still need a rule when the form loads to switch them to a read only view. You can copy your existing view (ctrl-a, switch to new view, ctrl v) anmd set view properties to read-only in 2010.
For SharePoint, I recommend creating a simple reusable SharePoint workflow with an Impersonation step that removes the item permissions for the submitted form.
All easy and quickly doable,