Existe un faq sobre este tema en la web de steam www.steampowered.com
Si no puedes recuperar la cuenta de ninguna manera siempre podrás enviar tu cdkey (donde viene impresa) a Valve pidiendoles que te liberen la cuenta.
Al menos eso creo recordar que ponía en el faq. Claro que con lo que cuesta el juego (14€), y con lo poco -esperemos- que falta para el HL2 no se si merece la pena armar este lio.
Do you still have your original retail package with the printed CD key?
If you still have your original printed CD key, we can reset your key. This will remove it from the account that is currently using it, and add it to your account. To do this, you will need to have a working Steam account (create a new one, if you don't have access to your old account).
Attention: Please note that we do not return the items we receive, so please do not send the CDs. Send the information typed and printed, and specify the use of any numbers in the names or email accounts (for instance, "B0B" has a number zero in it, please point this out to us). If your submission is handwritten, keep in mind that it will take more time to process the information. Also, documents received with incomplete information (eg. no account name, name or email address) will not be accepted and we will dispose of them with no warning.
You will need to mail us (by postal mail, not email):
The original printed CD key (not the whole package, just the part with the CD key printed on it). Please note that we need the original CD key-we are unable to accept copies or photos.
Your email address
The Steam account that you want the CD key assigned to.
Send your package to:
CD key reset
Valve Software
PO Box 1688
Bellevue WA 98009
USA