Let's go back. You had written
I performed the steps in this article -- reinstalling v10.6.8 and then reinstalling Security update 2012-004, but Mail still won't open.
Which article was that? Was it the Apple article on fixing this?
You just found a Mail icon on the Desktop after running the combo and sec updates again? You don't have Mail.app in /Applications?
Can you post a screenshot of that icon, Cmd-Shift-4, and use the camera icon above.