This is how you delete your Facebook account:
Go to http://www.facebook.com/help/contact.php?show_form=delete_account
Enter user name and password
Confirm that you want to delete the account
Enter your password again and enter the shown captcha word
Your account is then deactivated for 14 days. If you logon to your account before then end of the 14 days then the account deletion will be aborted.
After 14 days all your data and your Facebook profile will be gone.