Although I'm no Debian person (using Mandriva at the moment) I believe the command "chkconfig" works across distros. Log in as root, and type:
That will give you a list of all of the services you've got set up in your init.d section. Then you can just say:
chkconfig [servicename] off
to turn a service off. Conversely you can use "on" to turn it back on. But I'd be careful - some are very necessary of course!
Alternatively though - I'd investigate looking at your network setup to change the way your network devices work. In your network settings there'll be an option with each interface that allows you to specify whether or not you want to start it on boot.