Here is a script that will do it for you:
code:
Break ON

$sIPAddress="a.b.c.d"

While "true"
   Shell '%COMSPEC% /C ping -n 1 ' + $sIPAddress + ' | find "TTL=" >/dev/null'
   If @ERROR=0
      $Null=MessageBox("IP Address " + $sIPAddress + " is responding","It's Alive!")
      Exit 0
   EndIf
   Sleep(60)
Loop
Set $sIPAddress to the address you want to monitor.

This will check every 60 seconds, and popup a window when the IP address responds then exit.

Change the MessageBox() to "Beep" or "Play" to have a sound instead.