A. As long as the service is set to auto it will start when the server starts, but if SQL and the Agent are shutdown manually then the Agent won't auto-start when SQL does. You can run the following proc or enable it as a startup stored-proc to overcome this. (This will only work with Window NT/2000 as Win9x does not support services).
CREATE PROC AUTOAGENT
EXEC XP_CMDSHELL 'NET START SQLSERVERAGENT'
SP_PROCOPTION AUTOAGENT, STARTUP, TRUE