user-messages is an application for allowing users of your Django site to send messages to each other.
Include user-messages in your requirements file and add "user_messages" to your INSTALLED APPS setting.
Once you have the user-messages installed, hook up the URLs:
urlpatterns = patterns("", # some cool URLs (r"^messages/", include("user_messages.urls")), # some other cool URLs )
Now all you need to do is wire up some templates.