If you've just installed something and want to make sure it starts on boot then the init.d script needs adding to the various run level folders as a symlink. It's a bit of a drag and it can be sometimes forgotten.
Never mind, Debian comes with a handy script: Lets assume that we have a script in init.d called food (that's foo daemon) and we want it to start with a prioiry of 75 for run levels 2 3 4 and 5, we can simpley run:
[code]update-rc.d food start 75 2 3 4 5 .[/code]
Magic