Basically, this script was requested in forum's mIRC snippet request so I decided, what the heck, I'll drop it here too :)

Anyway, open up the dialog, turn on highlighter, enter highlight words, choose methods you wanna be informed with, when highlighted, and enjoy :)

;Alias part
alias hlight dialog - $+ $iif($dialog(hlight),v,m) hlight hlight

;Dialog
dialog hlight {
  title ".::Highlight Script by XperTeeZ::."
  size -1 -1 190 123
  option dbu
  text "Highlight Script by XperTeeZ", 1, 60 4 68 8, disable
  box "Highlighted words", 2, 7 20 54 70
  box "", 3, -4 -1 198 14
  box "Preview and Settings", 4, 2 13 185 83
  box "Settings", 5, 65 20 117 70
  box "ON/OFF", 6, 70 27 46 28
  radio "ON", 7, 72 34 23 10
  radio "OFF", 8, 72 44 23 10
  list 9, 9 28 49 60, size sort
  box "Add highlight", 10, 131 27 46 28
  button "Add Highlight", 11, 134 37 39 12
  box "Delete highlight", 12, 70 56 46 28
  button "Delete", 13, 73 66 39 12, disable
  box "Color (0-15)", 14, 131 56 46 28
  edit "", 15, 144 67 20 10
  box "Copyright", 16, 2 97 78 23
  text "Copyright © XperTeeZ, 2009  All Rights Reserved", 17, 6 104 71 14, disable
  box "Finally, SAVE the work :)", 18, 82 97 104 23
  button "Save everything I just did in here :)", 19, 87 105 95 12, default ok
  edit "", 20, 93 29 50 10, hide autohs
  text "Word", 21, 67 31 18 8, hide
  check "Echo to the active window", 22, 67 60 76 10, hide
  check "Display in @highlight", 23, 67 75 60 10, hide
  text "Sound", 24, 67 46 18 8, hide
  edit "", 25, 93 45 50 10, hide autohs
  button "Browse", 26, 145 45 34 10, hide
  button "Save", 27, 145 68 26 12, hide disable
}

;Init
on *:DIALOG:hlight:init:*: {
  didtok $dname 9 32 %hlights
  if (%hlight.status == on) did -c $dname 7
  else {
    did -c $dname 8
    did -b $dname 11,13,15,20,21,24,27
  }
}
;Single Clicks
on *:DIALOG:hlight:sclick:*: {
  if ($did == 7) { set %hlights.status on | did -e $dname 11,13,15,20,21,24,27 }
  if ($did == 8) { unset %hlights.status | did -b $dname 11,13,15,20,21,24,27 }
  if ($did == 11) { did -h $dname 6-8,10-15 | did -v $dname 20-27 }
  if ($did == 13) {
    if ($did($dname,9) { set %hlights $remtok(%hlights,$did($dname,9).seltext,1,32) | remini hlights.ini $did($dname,9).seltext | did -r $dname 9 | didtok $dname 9 32 %hlights }
  }
  if ($did == 26) { did -ra $dname 25 $sfile(C:,Select Highlight's sound,Use this sound) }
  if ($did == 27) {
    writeini hlights.ini $did($dname,20) echo $iif($did($dname,22).state == 1,on,off)
    writeini hlights.ini $did($dname,20) window $iif($did($dname,23).state == 1,on,off)
    writeini hlights.ini $did($dname,20) sound $iif($did($dname,25),$did($dname,25),none)
    set %hlights $addtok(%hlights,$did($dname,20),32)
    .echo -q $input(Highlight successfully added!,io,Success!)
    did -r $dname 20,25
    did -u $dname 21,22
    did -v $dname 6-8,10-15
    did -h $dname 20-27
    did -r $dname 9
    didtok $dname 9 32 %hlights
  }
}

;Remote...
on *:TEXT:*:*: {
  haltdef
  if (%hlights.status) {
    var %i 1
    while (%i <= $numtok(%hlights,32)) {
      if ($istok($1-,$gettok(%hlights,%i,32),32) == $true) highlight $gettok(%hlights,%i,32) $nick $1-
      inc %i
    }
  }
}

alias highlight {
  if ($readini(hlights.ini,$1,echo) == on) echo -a 4<HIGHLIGHT> < $2 >: $3-
  if ($readini(hlights.ini,$1,window) == on) { $iif(!@highlight,window @highlight) | aline @highlight 4<HIGHLIGHT> < $2 >: $3- }
  if ($readini(hlights.ini,$1,sound) == none) halt
  else play $ifmatch
}