I actually just went in and dumped the old tables (jos_sb_messages & jos_sb_messages_text) from the old db and inserted them into the new tables (same names, just fb instead of sb) and that worked for me. I took the sb dump file, renamed the commands for those two tables to fb, emptied the existing fb tables, and inserted the data through phpmyadmin (or do it through the shell, either way)...
The files I linked to got the users all transferred though, which was HUGE. Then all I had to do was sync users through CommunityBuilder and they all dropped into place with no problems...
Good luck...
