Authorization for navigation in Content Repository

Hi,

I have a problem with authorization restriction on SAP portal. When a user is created on SAP R/3 in the SAP portal I see that it is assigned to the role Everyone and I can't delete him from this built-in role. I want to make some restriction on the content repository but with the role Everyone a new user can see all that Everyone see, I'd like to use something that say:

"this folder can be accessed from Everyone except ..." I don't know how to implement the funciont except on the portal authorizations.

Thank you for the attention,

Luca

Bye.