The iPhone Dev-Team released RedSn0w 0.9.8b5 that supports tethered jailbreak for the most recent iOS 5 beta 5:
redsn0w has been updated to 0.9.8b5, adding support for Apple’s new iOS5 beta5 (point it directly at the beta5 IPSW). Please use this only if you’re a jailbreak app developer with a legit Apple dev account, and remember it’s a tethered jailbreak for now!
You can download RedSn0w 0.9.8b5 for Windows and Mac OS .