For those who didn't know, SpringBoard is the home screen of the iOS, the screen where all of your apps are located. I won't tell very much about Limera1n or GreenPois0n, they are just jailbreaking applications (Limera1n works on Windows and Mac, while GreenPois0n has a version for Linux also). Basically, they are quite the same thing (they're using the same exploit), and they work with any iDevice running 4.0, 4.0.2 or 4.2 firmware.
They are both very easy to use, you just have to download, run, and click "Make it ra1n!", and you'll be told how to put your device in DFU mode in order to start jailbreaking your device. A problem experienced by some of the people who tried jailbreaking their iDevices was that there was no Limera1n/GreenPois0n icon on the SpringBoard after jailbreaking (even though the applications said that jailbreaking succeeded).
The idea is that iTunes (it doesn't matter what version it is, it just needs to recognize your device) must be kept running while jailbreaking. Don't ask me why, I also had that problem, and when I left iTunes running while I used Limera1n, my jailbreak succeeded (when you see that drop rain on your iDevice, it means that jailbreaking succeeded). Probably, there's something in iTunes which allows the device to receive data while in DFU mode.
Who would have thought that there's such an easy fix for this problem?