Ubuntu – How to upgrade Postgresql 8.3 database file to 8.4

I upgraded my Ubuntu 8.04 To Ubuntu 10.04. Unfortunately, the upgrade process also updated the Postgres 8.3 install to an Postgres 8.4 install. My feeling is that although database engine binaries have been updated, the database itself was not migrated, hence it can not be loaded by the 8.4. Since the 8.3 data format is not compatible with 8.4 format, altering postgresql.conf is not enough, nor can I use pg_dump with my 8.4 install.

I need a way to upgrade my previous base from 8.3 to 8.4, with no access to a 8.3 engine, only a 8.4.

Any clue ?

Thanks !