The following script sets up a timer to fire five (%rep) times in total and every time it fires, it connects three (%step) times to the specified server (%server) and joins the specified channel (%join):
Code
alias t1 {
  var %rep 5
  var %interval 61
  if ($timer(post271665)) .timerpost271665 off
  else {
    .timerpost271665 -io %rep %interval conn_ect | .timerpost271665 -e
  }
}

alias conn_ect {
  var %server testnet.ergo.chat
  var %port +6697
  var %join #test271665
  var %step 3
  while (%step > 0) {
    var %nick $+(test,$base($rand(0,9999),10,10,4)), %altnick $+(%nick,_)
    server -m %server %port -i %nick %altnick -j %join
    dec %step
  }
}
Start this script:
Code
/t1

Note: You'll want to change %server, %port and %join to suit your needs.

GNU Terry Pratchett - Looking for a mIRC help channel -> Check #mircscripting @ irc.swiftirc.net