You have to link a valid email address to your forum account mate. But it's not necessary when registering, you can just make up something and add @gmail.com and later on decide to change it to a valid one. The reason be that if you loss access to your account, you will need the email linked to your account to help you recover it and change to a new password.

If you do use a personal email address and don't want it to be public, you can toggle that of on your forum account settings.  Its there on your profile..