Here is how you could jailbreak iOS 4.3 firmware on Windows operating system. The jailbreak process is done with Sn0wbreeze 2.3 beta 1 tool. Sn0wbreeze helps you to preserve your baseband during iOS 4.3 jailbreak so that you could unlock your iPhone once Ultrasn0w is live in iOS 4.3 Cydia.
NOTE: This is a tethered jailbreak. So you need to use iBooty to put your iDevice into a jailbroken state on every reboot (Instructions given).
How To Jailbreak iOS 4.3 on Windows
2. Download iOS 4.3 IPSW for your device.
3. Download iTunes 10.2.1 from here.
4. Now follow the steps given here (from step 4 onwards) to jailbreak iOS 4.3 on any device (Just do according to what device you have).