Hello guys. I need some work done on a PHPBB forum.

I have a PhpBB installed on one of my websites, and I want when someone opens a new THREAD:

1. depending on the category he is opening the thread in, to have different custom fields to complete

OR (a simpler version)

2. whatever the category (it doesn't matter) the user will have to complete some certain custom fields.

Pls help me