Don't have much time to give all the details as I am working on the tutorial now; however,
This jailbreak, like the 1.1.2 jailbreak, comes as an upgrade. This means you need to have a 1.1.1 or 1.1.2 jailbroken phone already, before you can begin. .
STATUS UPDATE: It's working!!! You can find the tutorial here: How to Jailbreak and Update to 1.1.3 iPhone Firmware Using Windows