This may just be academic, but..

Remember that when you talk about the "format" of a date/time value, you're strictly talking about presentation.  No matter how the date/time is represented, the actual datetime datatype is stored as two numbers that specify the number of days since Jan 1, 1900 and the number of milliseconds since midnight.

As has already been posted, you can explicitly define which format to use in a CONVERT function, or use SET DATEFORMAT to set the default.