Templates and Definitions

Introduction to Templates and Definitions http://msdn.microsoft.com/en-us/library/ms980852.aspx

Creating a Site Definition from an Existing Site Definition http://msdn.microsoft.com/en-us/library/ms868598.aspx

Customizing Templates http://msdn.microsoft.com/en-us/library/aa151982.aspx

Major Schema Files http://msdn.microsoft.com/en-us/library/ms954092.aspx