It works like that?
I have looked at that one, but was turned off by the lack of a functional demo or trial. I want to be able to change settings in the demo so that I can see if what I want to do actually works.
There is a fork of Drupal called vbDrupal, whose purpose is to integrate vBulletin to Drupal. This is a single sign-in integration.
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What is vbDrupal?
vbDrupal is the fork project of the Drupal content management system. It integrates Drupal into the forum software vBulletin.
With vbDrupal, Drupal and vBulletin are interwoven together, with no changes to the vBulletin forum, and minimal changes to the Drupal core. vbDrupal offers the best of both worlds, a great forum and superb content/portal management. vbDrupal also comes with add-on modules that allow node creation from vBulletin threads, the ability to create recent post and vBulletin calendar blocks, as well as using vBulletin threads for commenting in Drupal.