just copy and put this thing into your remote section.
oh yeah enjoy it!

alias allnick {
  ;Name: /allnick
  ;Author: zonIRC
  ;Tested with: mIRC 6.21
  ;Syntax: /allnick <nick> <messages>
  ;Description: to send a message to all common chan which you and nick are on.

  if (!$comchan($1,0)) || (!$2) echo -saftc info * /allnick: Error!
  else {
    var %x = 1
    while ($comchan($1,%x)) {
      ;simply change msg to describe if you want an action text
      msg $v1 $2-
      inc %x
    }
  }
}