Up to now..there isn't a sure way of doing this as far as I know...I've seen people try and end up wasting money due to the process failing on them ..sadly..however I've done this and it works for me...but didn't work for one person..as far as I saw...but anyways..:
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1
Make sure your iPod is running .3 or .4 firmware, which is the two latest versions. You can see this when you connect your iPod in itunes. If it is not the newest firmware, upgrade!
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Step 2
First, go to http://download.ziphone.org/ and download either the Windows or Mac version of the jail breaking software, depending on your system. It is 18MB in size, so it may take a couple minutes to download. When you are finished, open the installer, and extract the files to a folder somewhere on your computer.
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Step 3
Go to the folder you unzipped ZiPhone to, and open the bottom file, "ZiPhoneGUI.exe"
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Step 4
Make sure your iPod is connected via USB cord, and then hit the "Jailbreak" button on the left side of the interface.
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Step 5
Leave your iPod connected and let ZiPhone work it's magic for a couple minutes until it is done.
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Step 6
That's it, your done! Unplug your iPod and enjoy your new freedom