[@netweb Keymaster 13 years, 8 months ago]

I would look updating whatever it is holding you back from upgrading to WordPress 3.5.1 for the security fixes 3.4 & 3.5 have introduced at a bare minimum.

That said give it a try on a test site and if that works use the builtin WordPress Import/Export tool to export all the forums, topics & replies and then import them https://codex.wordpress.org/Importing_Content#WordPress