This diagram shows how a client (browser) or application (similar to an exe application) would gain access to the Vista system using a three tier solution.

This diagram shows how multiple users (clients) access the system.  Access to the system would take one of two of the following routes:

1) User session that prompts for access/verify codes.
2) Kernel session that allows queries prior to a user session being established or queries not requiring a "user" sign-on.  These queries could include things such as: System status and Introductory text