These are instructions on how to jailbreak your iPod Touch 3G and iPod Touch 4G using Greenpois0n for Mac. Greenpois0n supports iOS 4.1 and iOS 4.2.1 firmware. Use Limera1n if you want to jailbreak iOS 4.0, iOS 4.0.1, iOS 4.0.2.
Open your web browser of choice and navigate to http://www.greenpois0n.com. Click the Mac link at the bottom of the screen.
When prompted save the download to your desktop
Double click the downloaded greenpois0n-osx_rc5.zip file to extract the archive. Quit iTunes then double click greenpois0n from the desktop to launch the application
Connect your iPod to the computer, power it off, then click the large Jailbreak button
You will now be instructed on how to place your iPod into DFU mode. You can get help with this here.
You will be asked to press and hold the sleep button for 3 seconds.
Continue holding sleep; press and hold home for 10 seconds.
Release sleep button; continue holding home for 15 seconds.
Once your iPod is successfully in DFU mode the jailbreak will begin.
Click the Complete button once the software application has completed.
You'll notice some verbose mode text scrolling on your device.
After the iPod restarts you'll notice a new Loader application on your Springboard. Press to launch it.
Press to select Cydia then press the large Install Cydia button that appears.
Once Cydia has installed successfully you can remove Loader from your device. Press the Options button then press the Remove Loader.app button.
Reboot your iPod then run Cydia. Let it do all the necessary updates.
***A big thanks goes everyone who made this jailbreak possible.