The ADO.NET Entity Framework enables you to define an Entity Data Model (EDM) that includes object inheritance. The following links are to topics relevant to specific types of inheritance scenarios. This documentation does not feature all supported inheritance models. For more Entity Framework scenarios, see Application Scenarios (Entity Framework).
Table-per-type inheritance:
How to: Define a Model with Table-per-Type Inheritance (Entity Framework)
How to: Create and Execute Object Queries using Table-per-Type Inheritance (Entity Framework)
How to: Add and Modify Objects with Table-per-Type Inheritance (Entity Framework)
Table-per-hierarchy inheritance:
How to: Define a Model with Table-per-Hierarchy Inheritance (Entity Framework)
How to: Create and Execute Object Queries using Table-per-Hierarchy Inheritance (Entity Framework)
How to: Add and Modify Objects with Table-per-Hierarchy Inheritance (Entity Framework)
Other advanced data models:
Defining Advanced Data Models (Entity Framework Tasks)
Querying Advanced Data Models (Entity Framework Tasks)
Working with Objects from an Advanced Data Model (Entity Framework Tasks)
Erick Thompson, the ADO.NET Program Manager shows how you can do TPC. But it seem not to be supported in the entities designer:
http://blogs.msdn.com/adonet/archive/2007/03/15/inheritance-in-the-entity-framework.aspx