I installed my Bitcoin client after i baught my coins,
To open a HappyCoins Account you need to enter:
Your E-mail address
A Bitcoin address of your private wallet, so HappyCoins can send you Bitcoins (back)
Your IBAN bank account number, so HappyCoins can pay the Bitcoins you sell (for non-Dutch bank accounts also the name of the account holder is needed)
What did you enter when you opened up a HappyCoins Account, if you installed the client later?
The address from that email received those bitcoins, questionable if it's yours.
Tried to contact those HappyCoins guys? Never heard of that site before.