well i it did finally by exporting the threads and user file as csv files from discuss, then importing them into ms excel, sorting and adding the missing colums needed for vbulletin and then saving it again as a new csv file and then uploading it with phpmyadmin to the vbulletin databank. it took me approx. 1 week for 6000 posts with approx. 200 users.
I never want to have to do that again though
greetings tina