Sorry to dig up an old thread, but this thread was returned by Google when I was looking at getting the same information, and I have something to add to assist anyone else stumbling across this tread looking to read the AuditLevel via script.

Use xp_instance_regread instead of xp_regread when looking for info in the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer branch of the registry, it will sub in the correct instance syntax.

DECLARE @AuditLevel int

EXEC master..xp_instance_regread

@rootkey='HKEY_LOCAL_MACHINE',

@key='SOFTWARE\Microsoft\MSSQLServer\MSSQLServer',

@value_name='AuditLevel',

@value=@AuditLevel OUTPUT

SELECT @AuditLevel