Create A Forum - Support Forums

Ok.. so with the possibilities & impossibilities

• I was wondering if there is anyway possible to have a drop-down box for members to select when they sign up... for:
  
  What type of membership they would like :
  1. Film Makers
  2. Schools
  3. Tourism
  4. etc
  5. etc

From there on.. they will only be able to see forums and post that pertain to that group.. and news for all groups in general.
I know I can assign them to permission groups after registration.. but looking for an alternative upon registration  

Mainly so that forum doesn't get too cluttered for all members & also that I don't have to create too many Sites.
Anyone have any ideas?
Thanks