Code:
on ^*:JOIN:#:{
  if ($window(@events) == $null) window @events 60 100 600 200
  echo @evens $nick ( $+ $address $+ ) has joined $chan
}
on ^*:PART:#:{
  if ($window(@events) == $null) window @events 60 100 600 200
  set %partmsg $1-
  if (%partmsg == $null) { set %partmsg $nick }
  if ($window(@events) == $null) window @events 60 100 600 200
  echo @evens $nick ( $+ $address $+ ) has left $chan ( $+ %partmsg $+ )
}

something like that? the "^" hide the default message. this goes to your remote "ALT + R" in mirc.