Jailbreak utility RedSn0w 0.9.6 b5 is available for both Windows and Mac OS X. The process is the same on both operating systems. So you can use redsn0w tutorial for windows. There is only one major difference – download redsn0w for Mac OS hereor here.
iH8sn0w has just released a new version of Sn0wbreeze, the Windows tool that allows you to jailbreak Firmware 3.1.3. This is a small update that fixes a problem that occurs only on 64bit operating system.