where shld i do to allow eg, the starting of Sendmail during boot up... ???

What distro of linux? Mandrake,slakware,redhat?

redhat 7.1

use ntsysv as root to pick what starts and does not start in the current runlevel. If you want to change what starts in other runlevels use: ntsysv --level 1-5 whatever runlevel you want to modify.

or you can go into /etc/rc.d/rc<1-5>.d and either move or put a . in front of the S to stop a service from starting on boot up. If the service you want to start has a K in front of it and you want that service to start automaticaly change the K to a S.

to figure out what runlevel you are in type runlevel.

RH7.1 also uses xinetd. the config files for programs that use this are located in /etc/xinetd.d/