http://www.youtube.com/watch?v=hA9Fn4WCQvo&feature=player_embedded

As mentioned earlier, Redsnow has gone through a major update which is now live. The update brings alot of new functionality, most importantly IPSW files are no longer needed. When the device enters DFU mode, Redsnow recognizes your device and firmware, downloads the required files from Apple servers (for jailbreaking) and jailbreakes your device. The files are then cached for future use. This works for all firmwares uptil iOS 4.3.5 (Beta releases need to be manually jailbreaked) and all devices except the iPad 2 which can only be jailbroken using JailbreakME 3.0 on iOS4.3.3.

You can download Redsnow from here for Windows and Mac.