As shown in the picture [1], .NET Framework 3.0 is essentially a set of new libraries for the Vista platform. It is running on underlying 2.0 technologies, including the CLR and base classes.
The CardSpace component proposes to provide secure digital Identity Management, and is said to be complementary with other identity technologies such as OpenID.
[1] http://en.wikipedia.org/wiki/.NET_Framework_3.0#.NET_Framework_3.0