You mentioned apassword, but this should work without one. It takes advantage of the user levels in mIRC. I assume you wanted to give special users the ability to invite others users to the channel, without them being an operator or half-op? If so, I've created the following snipplet:

Code:
; !add <name>
; Adds user to invite allow list
on *:TEXT:!add &:[color:blue]#CHANNEL[/color]: {
  if ($nick ishop #) || ($nick isop #) {
    if ($ulist($2,invite,0)) {
      notice $chan $2 is presently on the invite allow list.
    }
    else {
      auser -a $nick invite Invite Allow List
      notice $chan $2 has been added to the invite allow list.
    }
  }
}
; !remove <name>
; Removes user from invite allow list
on *:TEXT:!remove &:[color:blue]#CHANNEL[/color]: {
  if ($nick ishop #) || ($nick isop #) {
    if (!$ulist($2,invite,0)) {
      notice $chan $2 is not on the invite allow list.
    }
    else {
      ruser invite $2
      notice $chan $2 has been removed from the invite allow list.
    }
  }
}
; !invite <name>
; Invites a user to the channel
on *:TEXT:!invite &:[color:blue]#CHANNEL[/color]: {
  if ($nick ishop #) || ($nick isop #) {
    invite $2- $chan
    notice $chan .... 11,1 $2- Has been invited to #CHANNEL by $nick .
    notice $2 9,1 You have been invited to join #CHANNEL
  }
}
; !invite <name>
; PERSONAL MESSAGE (/msg <bot> !invite <name>)
; Inites a user from outside the channel, assuming they are on the allow list.
on invite:TEXT:!invite &:?: {
  var %chan = [color:blue]#CHANNEL[/color]
  invite $2 %chan
  notice %chan .... 11,1 $2 has been invited to %chan by $2 $+ .
  notice $2 9,1 You have been invited to join %chan $+ .
}


If I'm off base, or still would like a password setup, let me know. I'll see what I can setup. This is, to the best of my knowledge, what you were aiming for. Be sure to change the channel names marked in blue.

-KingTomato