The Dev-Team has released the Windows build of redsn0w for a tethered jailbreak on the recently released iOS 5 beta. Keep in mind that this jailbreak (and iOS 5 beta in general) is intended for developers to get their applications ready for the official release—not end users. Most tweaks in Cydia will not work or be extremely buggy, so it’s best to wait it out until a later date. If you depend on an unlock, remember that updating to iOS 5 will upgrade your baseband.
Update: since apparently Apple now provides Windows iTunes 10.5 for iOS5 and iCloud developers, it’s no longer the case that only Mac owners can legitimately activate their devices. We now provide a Windows version of redsn0w for those developers (only!).
Redsn0w .9.8b1 will continue to work on all future iOS 5 betas as long as you point redsn0w at the beta 1 firmware. There is no ETA on an untethered jailbreak, though comex has posted a teaser over at Jailbreakme.com suggesting that a new PDF vulnerability has been found.
The Mac version of redsn0w was made available to beta testers last week.