Moving DB from Old WordPress to new WordPress

Hello,

I have to support a working wordpress 3.0.3 in quite bad shape.
Outdated WP, outdated plugin, lots of empty tables, errors and slowliness, etc.

My idea was to install a brand new WP, get updated plugin and to duplicate the DB.

Installing went right in minutes.
Duplicating and setting the DB is HELL !

I can’t duplicate using ssh cause hoster policy.
I tried using export/import with phpmyadmin and post get truncated.
I tried using the plugin import worpress and got internal error (i don’t have access to the error log).

A simple action turn out to be a real nightnare !!!!

May be i miss something and there is a simplier way to do the right thing.

Any advise will be appreciated.

Bernard