Lost Username, password or CD key
Username & password
If you still remember what E-Mail you used to register the game, you can use this link:
https://account.ea.com/myacct/view-download...&app=myacct
Just click first on "Forgot username?" and type in your E-Mail address used to register the game.
After you received an E-Mail with your username, click on "Forgot password?" and type in your just received username. It will send you another E-Mail with your password.
Now, you should be able to get online again.
CD key
You can find your used serial key(s) for each account you have registered on EA's official website. Enter your username and password (the one you also use to login to BfME online). A new mask will pop up and asking you to type your password in again. Do it and your account information will open. Now click on the "My Games" tab and scroll down a bit. Below the "My EA Games" headline you will find your registered game plus its key. Oh, and maybe you've noticed, at the first page you can also find all of your created nicks.
Important update
If you can't login on the page mentioned above, go https://support.ea.com. Click on Login, use your account name and password to login, then click on "My account". It will redirect you to exactly the same page, but now it should work!
A second option that requires no EA in any way, recovering your serial before uninstalling of the game:
Posted by Rainmaker. Read the original topic.
(tested for Win XP Home, don't know for sure about Vista)
I warn that you SHOULD NOT edit anything in the registery editor unless you're completely certain of what you're doing. It may cause serious problems with your machine!