[Dagoor]

In phpbb i did this with a mod. but I believe you can create user groups in vb and assign users with certain post to those group and then permission them they way you want them to behave.

for example:
you create a group, and assign it to include all the users who has less than 50 posts. (GroupA)
then you create another group who includes users with more than 50 posts (GroupB)
you set a permission to allow only GroupB to create topics or polls or whatever.

this is also usefull to give names to users with certain amount of posts.