iPhone Dev-Team has just released Redsn0w 0.9.6rc8 for Windows and Mac OS X users. Like previous versions, Redsn0w 0.9.6rc8 can jailbreak iOS 4.2.1 on iPhone 4, iPhone 3GS (Old+New Bootrom), iPhone 3G, iPod Touch 2G (MC+MB Model) & iPad (Wifi+3G). The only difference is that Redsn0w 0.9.6rc8 can now notify if the given PNG image for the custom tethered boot logo is a valid image file or not.
Again its a tethered iOS 4.2.1 jailbreak for iPhone 4, iPhone 3GS (New Bootrom), iPod Touch (MC model) and iPad (Wifi+3G). However iPhone 3GS (Old Bootrom), iPhone 3G and iPod Touch 2G (MB Model) users can enjoy full untethered iOS 4.2.1 jailbreak on their devices. Before using Redsn0w 0.9.6rc8, make sure you don't rely on an unlocked iPhone as jailbreaking your iPhone with Redsn0w will also upgrade its baseband to a version which might not be unlockable with the current version of Ultrasn0w.
If you don't rely on an unlocked device, just follow our step-by-step guide here to jailbreak your iPhone, iPod Touch or iPad with Redsn0w 0.9.6rc8.