Just don't use a var:

Code:
  
on *:TEXT:*:#:{
  if ($me isin $1-) {
    if ($window(@Private) == $null) { window -ng1 @Private }
    aline -hp @Private $time(HH:nn:ss) $date(m/d/yyyy) 13ChanMessage: <3 $+ $chan $+ 12\4 $+ $address($nick,5) $+ > $1-
  }
}