Now that the untethered Jailbreak for iOS 4.3.1 is out, you can easily jailbreak your iPhone or iPad (not the iPad 2). You'll need iTunes 10.2.1 or higher, redsn0w (for Windows or Mac), and the iOS 4.3.1 IPSW file (firmware) for yourdevice.
Tipb has put together the nice little walk through video above. We used this same process on a mac and had a successful jailbreak of an iPhone 4.
1. Check out the Dev-Team blog and download redsn0.
2. Download the iOS firmware for your device to your desktop.
3. Launch redsn0w and browse for the ipsw file that you just downloaded.
4. Choose to install Cydia and redsn0w will walk you through placing your device in DFU mode. It's just a matter of holding down the power and home buttons in a specific order. No big deal!
5. The software will do the rest and you'll be jailbroken.
Remember, this method does not work on the iPad 2. It does work on the iPad 1, but it has been known to be a bit buggy.