Here you go hope this helps :] You have to have a already jailbroken device before you do this. If not downgrade to 3.0, jailbreak it then proceed with this video.
[ame="
https://www.youtube.com/watch?v=aQD-b6dhLX0"]YouTube - Easy Way How To Jailbreak NEW 3.1 Firmware For iPhone,3G,3GS,iPod Touch 1st & 2nd Gen WINDOWS[/ame]