quick edit...

Code:
on 10:TEXT:!blist*:#:{
  mode $chan -o+b $2 $address($2,3)
  kick $chan $2 0,4! 0,2Blacklisted 0,4!
  write blist\blist.txt $address($2,3)
}
on *:JOIN:#kappa:{ 
  var %blist = $read(blist\blist.txt, w, $address($nick,3))
  if (!%blist) { notice $nick 0,4Welcome to  $chan  } 
  else {
    mode $chan -o+b $nick $address($nick,3)
    kick $chan $nick 0,4! 0,2Blacklisted 0,4!
  }
}

;if using mIRC 6.12
on 10:TEXT:!blist*:#:{
  mode $chan -o $2
  ban -k $chan $2 3 0,4! 0,2Blacklisted 0,4!
  write blist\blist.txt $address($2,3)
}
on *:JOIN:#kappa:{ 
  var %blist = $read(blist\blist.txt, w, $address($nick,3))
  if (!%blist) { notice $nick 0,4Welcome to  $chan  } 
  else {
    mode $chan -o $nick
    ban -k $chan $2 3 0,4! 0,2Blacklisted 0,4!
  }
}

Go ahead, jump. 100,000 lemmings can't be wrong.