[vijayninel]

You could try writing in a plugin for that:

Product : vbulletin
Hook Location: newreply_post_start
Title : vijay's great plugin
Execution Order: 5 should be ok
Plugin PHP Code:

PHP Code:

if (in_array($vbulletin->userinfo['userid'], array(1,2,3,4)) AND $threadinfo[forumid] != XX)
{
    print_no_permission();
} 


replace 1,2,3,4 with the members id and xx with the forum id.