Last week, i had to change, after install, the default language of SQL Server 2005 for display date in italian format (dd/mm/yyyy) and not for US format (mm/dd/yyyy). After many restart, i have found a solution. I changed language fields in regedit, replacing 1033 with 1040:

• HKLM\SOFTWARE\Microsoft\Microsoft SQLServer\90\Tools\ClientSetup\CurrentVersion
• HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\90\Tools\Setup
• HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL.1\Setup
• HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL.1\MSSQLServer\CurrentVersion

I have found this solution here: http://coolkidsdoit.wordpress.com/2009/01/28/changing-the-default-languagelocale-sql-2005/