Looking for some newb help with promotions. Desperate! Thanks!

[deadhook1]

I am desperately trying to change the permissions so that brand new members cannot post in one of my forums. They can have the same access as all registered members to the other forums, but..there is just one forum I need to make sure they can't post in until they've been registerd for 20 days and made 20 posts. I've tried to ask on the forums, read the user guide and played with it myself, but am still having trouble.

As it is now, all members (besides mods and admins) are all just in one user group.

I know where I go to the permissions, promotion and usergroup manager in the Admin CP, just don't know how to make this work.

Btw, I don't user "Reputations" on my forum for my members and don't really want to.

I don't want to change anything for the other user groups, just make that change.

I know I have to add a new promotion, but am not 100% certain how to do this properly to achieve what I'm trying to achieve.

I don't understand what the "Reputation Level" is either.

Can someone walk me through how to do this properly?

I CAN'T THANK YOU ENOUGH FOR ANY HELP...THIS IS SOMETHING PRETTY IMPORTANT TO ME AND I'M HAVING A HARD TIME WITH IT.

THANK YOU SO MUCH!!!!!!!!!!!!!!!!!!!!!!!!!