If you havnt patched the game, you can find your key in the registry @ HKEY_LOCAL_MACHINE\SOFTWARE\Electronic Arts\EA GAMES\Battlefield 2\ergc
If you have patched the game, you cannot retrieve it - because the patch encrypts your key.
yeah...cause noooooooooooooooooooooooo one is running a patch on BF2...its perfect right out of the box even now, eleventy billion yrs after the release...why would you want to patch the flop-prone headshots? or the uber 1337 g36e that makes even the nubbiest n00b a 1337 haxorz?
oh and good luck getting help from EA, buncha horses-asses there...can't even make a decent game let alone provide decent technical support...