I've tried grouping dates by week in Excel. Excel seems to want to group the 'weeks' alpha instead of based on actual date/time. Example below. Any advice? Or is it me.

2/28/2005 - 3/6/2005
3/14/2005 - 3/20/2005
3/21/2005 - 3/27/2005
3/28/2005 - 4/3/2005
3/7/2005 - 3/13/2005