I did a search in google for you, however most of the responses are saying that it can't be done (easily) or they're postings with paid jobs. You might want to check the freelancer.com boards and some of the similar paid job sites and hire someone to do the conversion.
From what I've read, PHP-Fusion is more than just a CMS, it's a forum also - converting the users tables appears to have been the biggest challenge. It can be done, but you'll need to lay out both database schematics and then match them up correctly before importing one to another.
I'd recommend that you check out Joomla's forum and run a search for an import script there
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Actually,you'd better process this issue through phpmyadmin, because much trouble things will generate if you use the 3rd tools. All the operations associated with database could be done in phpmyadmin.
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Try running a search on Google for an automated import script, but manual is definitely the best way if you have the time.
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SwisSQL offers a complete Data Migration Tool that helps the migration and transfer of database schemas and data across leading databases such as Oracle, IBM DB2, MS-SQL Server, Sybase, MySQL, PostgreSQL and MS Access. It offers an open, user-friendly, and extensible migration process ensuring reliability and data integrity.