In my case, I just wanted to start up snmpd at boot time on Tiger. I had quite a hard time configuring launchd to do so, until I found out about the open-source Lingon program. Lingon is simply a graphical user interface you can use to configure launchd correctly. It includes an assistant, as well as a built-in text editor for editing.
In order to start a daemon, I just added a Users Daemon, into which I entered the following:
- Label: org.ucd.snmpd
- ProgramArguments:
- /usr/sbin/snmpd
- -c /etc/snmpd.conf
- Check RunAtLoad and enter a description.
No need to say that Lingon doesn't need to be running for all this to work ... and I have no doubt that plenty of very cool things can be done with this tool, as there are a lot of very cool features in launchd.

