How to set certain Create content - chat/chatroom settings as default

Hi,

Could you please tell me how I can set some of the fields on the create chat/chatroom page as default and remove/hide these fields from users.

For example the 'User Profile Picture Support' settings. I'd rather our users didn't have the option of setting whether or not pictures should be visible in chat. And also the 'Profile Picture Preset' has a list of imagecache profiles that are specifically for other nodes. I'd like to choose a default profile and remove this field entirely.

I'd like to have the set the Chat settings for update frequency, idle time and old messages, with users only been able to access 'Make this chat private' and 'maximum users allowed'

Thanks for your time!