Using aline -pi switches to to wrap and indent the text (and use the [c] parm to color it)
Also "if !$window()" in place of $iif(!...)
Code:
on ^*:notice:*:*:{
  if (!$window($+(@Notices-,$network))) { window -ael $+(@Notices-,$network) Arial 12 }
  aline -pi 4 $+(@Notices-,$network) ( $+ $nick $+ ): $1-
  window -g1 $+(@Notices-,$network)
  beep
  halt
}