When you signed up for Xbox Live, you had to provide or create a valid Windows Live ID to create your account. This is generally a hotmail or other windows live email address, and it isn’t necessarily the primary email address you receive notifications on.
To find your Windows Live ID, sign into your Xbox Live enabled profile on your Xbox 360. Hit the Guide button on your Xbox 360 controller and go to the Settings tab, then select Account Management, then Windows Live ID.
This will show you the email address associated with your Xbox 360 gamertag. If you don’t remember your password, go to http://www.passport.net and try to do a password reset.