Making a New 'post' count group

Hello... my question is I have several 'created' groups I,E. Special Admin, Founding Members and so on... that I have created and personally assign to these groups.

I was wanting to create a 'post count' group that rewarded frequent posters for contributing to my site by their constant posting/comments/etc.  I did so, and set the count like 20 posts... thinking that everyone that posted 20 or more comments already would automatically be transferred to this group.

But they did not change and are 'not' moved to that group.

Did I do something wrong or will such an idea as I had simply not work?

Help appreciated.  Thanks!

Beo

Post groups happen based on posting. It does not change the primary membergroup of the user. 

Okay, thanks for the reply but I am still a bit confused about the 'count' groups permissions... so, by setting up my NEW post count based group, will anyone that has already exceeded the count that I set, automatically be privy to the special room that I activated for that particular group?