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Download redsn0w 0.9.8b3: http://stateofjailbreak.com/tutorials/redsn0w-0-9-8b3-tutorial/
Find iPhone / iPod touch / iPad firmware files: http://stateofjailbreak.com/tutorials/find-iphone-firmware-files/
Jailbreak iOS 4.3.4 for iPhone 3GS & 4, iPod touch 3G & 4G and iPad w/ redsn0w 0.9.8b3
In this video I give a full tutorial on how jailbreak iOS 4.3.4 using redsn0w 0.9.8b3 on an iPhone 3GS (new and old bootrom), iPhone 4, iPod touch 3G (16GB and 32GB models only), iPod touch 4G and the original iPad 1. The iPad 2 is not currently supported. redsn0w 0.9.8b3 is a tethered jailbreak for iOS 4.3.4 and is available for both Mac and Windows.
If you use Windows Vista or Windows 7 then you will need to do an additional step to avoid any problems, errors or issues. Right click redsn0w 0.9.8b3 and under the Compatibility tab select Run this program in Compatibility Mode for Windows XP Service Pack 3 (SP3) as well as run it as Administrator.