Here we go with MediaMogul configuration options in RokBB3 panel:
Display right column - you can enable/disable displaying right column. With disabled right column and disabled joomla menu you can get full width forum.
Show joomla menu - this option will enable/disable a menu from your joomla instalation.
Joomla menu path - this is a path to directory for pre-generated joomla menu stored in .txt file. This is usually created by special component for joomla called RokBB3 Menu Generation.