password protection on files

hey guys, i really have no idea if this is the place to ask a Q like this, but im going to fire away anyways

i have a copy of warcraft 3 (my own copy that i PURCHASED) installed on my friends computer (he has 2), warcraft 3 is cd-key protected so if i want to play online i cant be on at home and on at his house at the same time, which is fine, because i cant teleport or be in 2 places at once. But recently the jerk has been using my cd key so he can play online and use his other computer for whatever else he wants, so when he does this i cant play, sometimes for hours.

so what im asking, is there anyway i can password protect the .exe file on his computer to stop him from using the game when im not there? right clicking in explorer doesnt give me a security option, so i guess im looking for a program or a different way of doing it - RUNNING ON WIN XP

ps :and yes i know i could just delete the game, but then id have to reinstall and update everytime i went to his house (takes about 30 mins)

pps : and yes what a crappy friend, i know i know everyone tells me