You will need to be root when editing the files. They are in /etc/rc.d/
For the ones that are properly named, such as rc.sshd you can just remove the execute bit from the file:
chmod -x rc.xxx
where xxx is the rc file you don't want executed during startup. For ones that are enclosed inside a runlevel init script, you will actually need to edit the rc file itself, usually I use # (comments) to block out the things I don't want rather than deleting it. This way if I want it back later, or I screw up my commenting somehow, it's not too hard to bring my system back.