By executing the below stored procedure, you can get/check SQL server authentication in XP mode:
DECLARE @AuthenticationMode INT
EXEC master.dbo.xp_instance_regread N'HKEY_LOCAL_MACHINE',
N'Software\Microsoft\MSSQLServer\MSSQLServer',
N'LoginMode', @AuthenticationMode OUTPUT
SELECT CASE @AuthenticationMode
WHEN 1 THEN 'Windows Authentication'
WHEN 2 THEN 'Windows and SQL Server Authentication'
ELSE 'Unknown'
END as [Authentication Mode]