Try this:
http://www.amazingbrass.co.uk/dist/exte ... -merge.zip
This is TOTALLY experminental. It should merge your Snitz forum with an existing PHPBB forum, but who knows - it might format your hard drive instead. Use at your own risk.
To try it, download the v0.3 converter from the first post in this thread, then replace Snitz2PHPBB.php with the file in the experimental zip, above.
If you do want to try it, I suggest the following:
1. Back up everything. Twice.
2. Take a note of a selection of posts in your PHPBB and Snitz forums. After the migration (if it works), make sure they are all still there.
3. If you get any errors, please post here again with as much detail as possible.
4. The script currently DOES NOT rewrite internal links when merging forums, so any links in posts to other posts in your forum will be wrong. If the script works, I'll fix this bit as it's very minor.
Good luck, and remember - I wrote this with zero testing on the back of a fag packet, so the odds of it working are slim