While the video still contains useful information, the process has changed slightly and the video hasn't been updated to reflect those changes. I suggest you just follow the written directions on the wiki page:

http://isboxer.com/wiki/WoW:Interact_with_Target

It literally comes down to:
  • Setting a key binding in game
  • Setting a hotkey for the IWT Key Map in ISBoxer (doesn't have to be the same key you just used, but it can be)
  • Setting a key for the IWT Variable Keystroke in ISBoxer (the same key you used in game)
  • Exporting your settings