iH8sn0w just released a new update for the sn0wbreeze (V1.6.2), it fixes the YouTube/iBook issues as well as Error to iTunes Restore Errors. You will require the following to carry out the jailbreak :

Download Sn0wbreeze V1.6.2 for Windows
Download iTunes 9.2 for Windows and Mac
Download iOS 4 original Firmwares
Download .NET Framework 2.0 (Needed to Launch Sn0wbreeze)

Just follow the on-screen instructions to Jailbreak iPhone 3GS, iPhone 3G, iPod 2G on iOS 4 Using Sn0wbreeze 1.6 [Windows].

After following the guide to Jailbreak, You will be Easily able to Unlock your iPhone 3GS on any Baseband Including 05.13.04 / 05.12.01 Using Ultrasn0w 0.93, Step by Step guide posted here.

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