The Windows version is not released yet due to it's slow compared to the Mac OS X version. So the iPhone Dev Team working on speeding it and release it as soon as possible.
The update follows as:
The fifth beta is now available (testers ONLY please!). Bluetooth is now working (and any sandbox-related issues should be resolved too). Please do not pirate the 4.2b3 IPSW! Only those enrolled in the iPhone Developer program have legitimate access to that IPSW using these links (http://pastie.org/1403214) (the links won’t work unless you’re a legit developer currently logged in).To use Redsn0w 0.9.7b5, use our guide posted here while removing STEP 4 since it doesn't required usbmuxd anymore.
There is actually a Windows version of beta5, but it’s excruciatingly slow compared to the Mac version because it’s forced to use files on your hard drive instead of RAM while it’s processing the very large IPSW images. It really is very very painfully slow, so we probably won’t be releasing it for testing purposes unless it can be sped up somehow.