As you already know, the Spirit Jailbreaking tool was released some time back and as promised here is a detailed guide to jailbreak iPod Touch 3G on OS 3.1.3 using Spirit untethered tool. Spirit works on both Windows and Mac OS X and can jailbreak all the newer iDevices like iPhone touch 3G and 2G (MC model), iPhone 3GS and the newly released iPad as long as they are officially activated via iTunes.
Using an untethered jailbreaking tool like Spirit, you do not need to re-jailbreak your iPod Touch every time you restart it (which is so annoying).
Make sure you backup your SHSH files before jailbreaking your iPod Touch 2G/3G using Spirit. Of course you can still jailbreak your device without backing up the SHSH files, but in case Apple patches this exploit, there will be no way you downgrade to 3.1.2 later on. This is why we keep reiterating how important it is to backup the SHSH files before each time you jailbreak. Check this guide to know how to save SHSH blob on your PC.
Guide to Jailbreak iPod Touch 3g/2g using Spirit
The process of jailbreaking your iPod Touch 2G and 3G using Spirit userland tool is very similar to the guide we just posted to jailbreak iPhone 3g/3Gs. So please follow the step-by-step procedure given in the article (linked below) and have your iPod touch jailbroken!