Try running "runlevel" to see the runlevel you're in (say it's 3), now run "chkconfig --list" to see what get's started in your runlevel or see the links with "\ls .etc.rc,d.rc3.d/S*", then for each service it says "on" (or result from ls) there are two ways to turn it of: using "chkconfig" (man chkconfig for more) to handle changing symbolic links automagically or manually. To disable it manually, first stop the service: "/etc/(rc.d/)init.d/<servicename> stop", then in the runlevel (rc#.d dir, 3 in this example) change the corresponding S??<servicename> link to read K??<servicename>, where the question marks are the place in the sequence the service gets started as.
Now the service wont get started next boot.
Run ls or chkconfig again to check.