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

Basically what Jntg4 said;

1) Create all of the boards for all of the forums.
2) Create each of the membergroups for the boards you made and give them customizable permissions.
3) Go to permissions and let each of them see the according boards
4) Now set it so each of the normal membergroups can switch to the others for free