Here you will find a session I did on SQL Server 2012 Windowing Functions. Should get you what you need. There are two other great sessions from me on that schedule page: Common TSQL Mistakes and SQL Injection.
http://www.sqlsaturday.com/249/schedule.aspx
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service