MOSS - Farm Hierarchy

Logical Components in a Farm

Farm Hierarchy

SharePoint Containment Hierarchy 

Single Sign On - Products

Single Sign-On (SSO) is a method of access control that enables a user to
log in once and gain access to the resources of multiple software systems
without being prompted to log in again. Single sign-off is the reverse
process whereby a single action of signing out terminates access to
multiple software systems.
As different applications and resources support different authentication
mechanisms, Single Sign-On has to internally translate to and store
different credentials compared to what is used for initial authentication.

Complete List of SSO products and its vendors can be found in link http://identityaccessmanagement.blogspot.com/2005/05/vendor-list.html 

SSO Products : Some of the SSO Products are
1. CAS enterprise single sign-on
2. Sun OpenSSO Enterprise
3. CA Single Sign-On
4. Tivoli Access Manager for Enterprise Single Sign-On - Its details can be found in http://www-01.ibm.com/software/tivoli/products/access-mgr-esso/
5. Novell SecureLogin
6. Entrust GetAccess
7. Sentillion - Is a Microsoft Company. It provides Vergence SSO. Details can be found in http://www.sentillion.com/expresso/index.html
8. Oracle Enterprise Single Sign-On Suite Plus - http://www.oracle.com/technology/products/id_mgmt/esso/index.html