When there is not yet a Drupal module for direct conversion from your current forum software, migration can often be done in two steps, via popular forums with many converters available. Possible procedures are for example:
- Old forum -> phpBB -> Drupal
- Old forum -> vBulletin -> Drupal
Migration to Drupal via phpBB
For the Old forum -> phpBB step, see phpBB 3.0.x Convertors and phpBB 2.0.x Convertors. If you need to install the old phpBB2 version, see Download legacy release (phpBB, like Drupal, is open source).
Migration to Drupal via vBulletin
For the Old forum -> vBulletin step, there are modules in vBulletin's ImpEx Import System to import from a large number of forum systems.
Features and performance
For a Drupal forum with features similar to those of well-known forum systems such as phpBB and vBulletin, see the Advanced Forum module.
The Migrating to Drupal handbook section includes general methods, and also sub-sections on migrating from specific software systems, such as forums and CMS.