Hi.
This is pretty simple.
Copy this into your remote, and do a "/events on":
on *:text:!onair:#channelname:msg $chan $read(COMPUTERNAME\\shareddir\path\file.txt,1)
This reads the first line. Change COMPUTERNAME\\shareddir\path\file.txt to the file path on the other computer. Example: if the other computer's name is "STORE", and the "C:\mIRC\" directory is shared with name "mircdir", and the !onair file is "C:\mIRC\onair.txt", you need to use this: STORE\\mircdir\onair.txt.
Bye