I was afraid this would happen.
I have NO mail or ability to use Mail after my upgrade.
All of my accounts and folders appear in the window but all of the contents are gone. Mail won't quit unless I use Force Quit. It will not send or receive emails. I'm glad I have a laptop for backup until I get this resolved. It's too late to call AppleCare.
I found instructions about correcting this but thus far the Rebuild option is not working.
Missing emails after installing Leopard? - TheAppleBlog
Like several people who posted I'm unsure where to move the three files from the library. I've drug all three to my desk and I can see that the files are still there, so I'm not in an all out panic.
Everything else about the install seems to have gone OK.