BleepingComputer.com: BF2 under multiple windows user logins

I have windows xp pro sp3 and installed BF2 under my user login. I created a player in battlefield for my son and can play him as long as I am logged into windows as me. If I log into windows as my son when I try to join a game it says cd key is invalid. Is there some files I can copy from my profile to his that will have the valid cd key? Have tried it with my sons profile as admin and not, doesnt help, also copied bf2 folder from my profile to his thinking cd key might be there.