I'm not too sure if this works because I don't have an FTP account so..
This is using Mavric-'s (Using FTP through mIRC without sockets.) tutorial. smile

Code:
On *:Text:!upload &:*: {
  if ($isfile($2)) {
    if (!$isfile(batch.bat)) {
      var %bat = write batch.bat
      %bat @echo off
      %bat -i -s:ftp.txt
      %bat exit
    }
    var %ftp = write ftp.txt
    %ftp ftp
    %ftp open your.ftp.server
    %ftp YourUsername
    %ftp YourPassword
    %ftp PUT $2
    %ftp QUIT
    run batch.bat
  }
}


-Andy