Update Sql Server from Mysql
You can't "see" the SQL Server from within MySQL like you can in the reverse direction with a linked server. 

The only way I can think of doing this is to create a MySQL trigger that calls a User Defined Function that executes an external application and passes the new data to it. The external application would have to connect to the SQL Server database and push the data to it. 

DELIMITER @@

CREATE TRIGGER Test_Trigger 
AFTER INSERT ON MyTable 
FOR EACH ROW
BEGIN

DECLARE cmd CHAR(255);
DECLARE result int(10);
SET cmd=CONCAT('/usr/bin/php ', 'home/sync/send_to_sql_server.php f1=', NEW.f1, ' f2=', NEW.f2);
SET result = sys_exec(cmd);

END;
@@
DELIMITER ;