This is an incredible article that describes indexes done by Paul Randal. It is the core to understanding how a sql server database stores data and how you must understand how it functions.

http://blogs.msdn.com/b/sqlserverstorageengine/archive/2006/12/13/more-undocumented-fun_3a00_-dbcc-ind_2c00_-dbcc-page_2c00_-and-off_2d00_row-columns.aspx