How to use launchd to schedule a script to run?

Try this...

Try a program called Lingon, it is available from the Apple website as well as the developer's page. It comes configured with a lot of system scripts and you can add your own. Actually, if I think about it, it reads the ones in your system and gives you access to them?? Someone might be able to clarify, thanks.
There are probably other solutions out there but I use this one. You can alter the 'pre-configured' ones but the usual precautions apply, be careful, especially if you are a newbie. But give it a go, cheers.