Hi Malte,
I created a DimDim integration with .LRN, called webmeetings package. I believe that to change this integration to the BigBlueBotton you need to change only the URLs in the code, because the API is similar to the DIMDIM.
Example:
To create an room, in DimDim you need this URL: http://yourdomain/dimdim/html/envcheck/connect.action?action=host&email=$user(email)&confKey=$webmeeting_key&displayName=$full_name&confName=$webmeeting_subject&lobby=false&networkProfile=2&meetingHours=5&meetingMinutes=0&maxParticipants=100&presenterAV=$one_webmeeting(type_key)&maxAttendeeMikes=3&returnUrl=[ad_url][ad_conn url]&whiteboardEnabled=true&screenShareEnabled=true
In BigBlueButton you need this:
http://yourserver.com/bigbluebutton/api/create?name=Test+Meeting&meetingID=abcdef&attendeePW=111222&moderatorPW=333444
You can see all the URLs to manipulate the software here:
http://code.google.com/p/bigbluebutton/wiki/API#Create_meeting_example
Get the webmeetings package here: http://www.openacs.org/forums/message-view?message_id=3501402
