Last day, the Sn0wbreeze 2.3 tool was released by iH8sn0w which could be used to jailbreak iPhone 4 iOS 4.3 on Windows OS. It also allows to preserve the baseband so that you could unlock iPhone 4 iOS 4.3 once Ultrasn0w is live on iOS 4.3 Cydia. Here is how to jailbreak iPhone 4 4.3 iOS on Windows.
Also Read : Jailbreak iPhone 4 4.3 iOS on Mac
NOTE : This is a tethered jailbreak. You will have to use iBooty on reboot.
2. Download iOS 4.3 IPSW for iPhone 4.
3. Download iTunes 10.2.1 from here.
4. Now follow the steps given here (from step 4 onwards) to jailbreak iPhone 4 4.3 iOS.