What distribution do you use? At least some(most?) include various utilities to make this easier than manually mucking around with symlinks in /etc/rc.d/* directories. It doesn't hurt to do that at least once though to help fully understand the structure and layout of how the average Linux machine does this.
On RedHat for instance though, there are graphical utilities to enable/disable "services", there is "ntsysv", there is chkconfig, etc...
# chkconfig snmpd --list
# chkconfig snmpd on