Upgrading from 3.4.8a (Postgres)

I have a simple Phorum 3.4.8a installation that uses Postgresql 7.2 as the
database. Now I'd like to upgrade the forum to version 5 (I have MySQL too on the
server). Any ideas how to achieve this? Maybe there is some way to convert the
3.4.8a forum to MySQL and then use the upgrade script?