You shouldn't need to transfer anything..... you are trying to make it very complicated when it's not... treat it like an upgrade.
Copy the new UBBThreads files to your existing wwwthreads directory. Do not overwrite main.inc.php, config.inc.php or theme.inc.php. Then run each altertable script (in the /install directory), from your current version to the last version which used altertables (6.4.1) then run the 6.5 upgrade utility (/install/upgrade.php) to complete the upgrade. All users and posts and data is preserved.
