Erm, copy the triggers first and go to Mushclient's File->Import... Uncheck all options except for 'Triggers', click on Clipboard. That will add the triggers to your world file.
Next you'll need to install the script. If you don't have a script file associated with your world already then open a plain text editor and paste the following into it:
option explicit
sub CountHits(name, output, wildcs)
dim tempArray
tempArray = split(name, "_")
select case tempArray(1)
case "hit"
hitsLanded = hitsLanded + 1
case "miss"
hitsMissed = hitsMissed + 1
end select
UpdateBar
end sub
sub UpdateBar
dim strn
world.InfoClear
strn = "Hits: " & cstr(hitsLanded) & space(5) & "Misses: " & cstr(hitsMissed)
world.Info strn
end sub
Save the file as AchaeaScript.vbs (or any other name with .vbs extension) somewhere in your Mushclient directory. Now go open Mushclient again and go to Game->Configure->Scripting (Shift+Ctrl+6). In the new window choose Vbscript as your scripting language, check 'Enable script' and click on the Browse button right below that option. Find your saved script file and open it. Click Ok in the Scripting window. Your script will be compiled and become available.
If you have a script file already then just paste the above script (except for 'option explicit' if you already have it also) into that file and save it.