I finally got around to upgrading. I ended up doing a clean install of Debian Squeeze 64 bit with Ispconfig 18.104.22.168.
I copied over the old /var/vmail directory and imported only specific tables from the dbispconfig database. Also copied over the roundcube database.
The tables that I imported from the mysql dump for dbispconfig were
Other than a few hiccups in various configurations it has gone fairly smoothly.