Here's one I wrote a while ago...

Code:
alias -l username return <your username>
alias -l password return <your password>

alias -l raiseerror {
  echo -a * /twitter: $1-
  halt
}
alias -l urlencode return $regsubex($1-,/([^a-z0-9])/ig,% $+ $base($asc(\t),10,16,2))

alias twitter {
  hfree -w twitter
  sockclose twitter
  sockopen twitter twitter.com 80
  sockmark twitter status= $+ $urlencode($1-)
}

on *:sockopen:twitter:{
  if ($sockerr) {
    sockclose twitter
    raiseerror socket error. Try again later.
  }
  var %s = sockwrite -n twitter
  %s POST /statuses/update.xml HTTP/1.1
  %s Host: twitter.com
  %s Authorization: Basic $encode($+($username,:,$password),m)
  %s Accept: */*, *.*
  %s Connection: close
  %s User-Agent: mIRC/ $+ $version
  %s Content-Type: application/x-www-form-urlencoded
  %s Content-Length: $len($sock(twitter).mark)
  %s
  %s $sock(twitter).mark
}
on *:sockread:twitter:{
  var %data
  sockread %data
  if ($regex(%data,/<error>(.+?)</error>/)) {
    hfree -w twitter
    sockclose twitter
    raiseerror $regml(1)
  }
  if ($regex(%data,/<(.+?)>(.+?)</\1>/)) hadd -m twitter $regml(1) $regml(2)
  elseif (%data == </status>) .signal twitterpost
}


Edit the username and password return values at the top, then use /twitter <status> to update your status.

When the post is complete you can use the "twitterpost" signal to do something, like so:

Code:
on *:signal:twitterpost:{
  var %i = 1
  while ($hget(twitter,%i).item) {
    echo -a $v1 : $hget(twitter,$v1)
    inc %i
  }
}