Doesn't sound update related. If it were the update, you would have lost Mail completely. See if running the 10.6.8 Combo update fixes the issue.
If this doesn't help:
First take screenshots of all your Mail settings, you will need to refer to these later. Next, with Mail closed navigate to your Home Folder Library>Mail and first make a backup of the entire Mail folder by option-clicking on it and dragging it to the Desktop.
Next, in the same Library, go to Preferences and find com.apple.mail.plist and, similarly, make a backup copy by option-dragging it to the Desktop.
You will know these files are being copied when you see a small green circle with a plus + sign in the middle. Just drag them to the Desktop, holding the mouse down, then release. The originals should remain where they are.
Next, still with Mail closed, move the com.apple.mail.plist to the Trash (but don't empty it yet.) Then open Mail and you will be asked and guided to set up Mail again. Here is where you refer to your screenshots.
Now, if none of this helps, you can return to your original Mail simply by replacing the new Mail folder with the backup one you made, and moving the Mail.plist back using File>Put Back from the Trash. Or, alternatively, just move the backup copy where it came from.
You might be able to get a new Mail by first trashing Mail, then running the Combo Update. I haven't tested this, although it's claimed it will do this.
Am I hallucinating about not receiving any disks with my MacBook Pro?
If this was a new, not used, machine, it should have come with those. Call Apple and they should offer to send you those for free.
Message was edited by: WZZZ