Consider this the official announcement: RPG Palace is converting software in a few days from IPB 2.1 to Drupal 6.19. This is more than just the forums; the entire site will be moved into Drupal, including existing news, tutorials, articles, and downloadable content.
Private messages will be lost. If you have any important information in your private messages, save it now.
Some users will need to re-upload avatars, though most avatars will transfer properly.