I have a datetime field in SQL Server 2008 which stores the date and time in military format (or international format if you prefer)
examples:
2011-
DateTime is stored in an internal representation - there is no format associated. When you need to display the DateTime, specify the formatting you want for converting the DateTime into a string.
It is much better to let the application decide on formatting than formatting in SQL.
See standard and custom Date and Time Format Strings for more information.