ipod os 3.1.2

How I can lower the iPod Touch OS 3.1.2 to 3.1.3?
I have a brand new iPod touch 3.1.3 that comes pre-installed. How do I downgrade 3.1.2 operating system because I can not do somthing in 3.1.3. Please be as specific as possible, and for how long will each download, if necessary.
You must download 3.1.2 http://www.hackouriphone.com/2010/01/get-free-firmware-upgrade-for-ipod.html connections depends on firmware, so online 4MBS, you can download in 10 minutes
Iphone 3G/3GS OS 3.1.2 Internet Tethering.
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