Dave,
I am struggling with the appearance of vBulleting within Moodle. So far we run vBulletin as a completely separate external installation and simply create a web link on the course homepage to the vBulletin forum that is appropriate to the course. If you run multiple courses and dont want each student to see each others forums this can be a pain as you have to set up each student in vBulletin. To get a single signon we use Jfusion which manages all the logons across Moodle Joomla and vBulletin.
You can find JFusion here: http://www.jfusion.org/
Hope this helps a bit.
All the best - Geoff.