The iPhone Dev Team is working on
iOS 4.3, iOS 4.3.1 untethered jailbreak. The iPhone Dev Team has confirmed the iOS 4.3.1 is safe for jailbreak, the jailbreak bugs are not pitched. Just
download Windows redsn0w 0.9.8 for iOS 4.3, iOS 4.3.1 untethered jailbreak.

Redsn0w 0.9.7b6 supports iOS 4.2.1 untethered jailbreak, the upcoming redsn0w 0.9.8 for windows and Mac will support iOS 4.3 untethered jailbreak, for the detail steps, you can refer to:
Redsn0w 0.9.7b6 to Untethered Jailbreak iOS 4.2.1 iPhone 4, iPhone 3G/3GS Tutorial. You need to change the iOS 4.2 firmware to iOS 4.3 firmware.
You can
download redsn0w 0.9.8 for windows,
redsn0w 0.9.8 for Mac from http:blog.iphone-dev.org. Well, the redsn0w 0.9.8 may not need the iOS 4.3 beta SHSH blobs any more, because the exploit used in redsn0w 0.9.8 may be different from redsn0w 0.9.8.
You may like:
Download Redsn0w 0.9.8 for iOS 4.3 iPhone 4, iPhone 3GS, iPad 2 Jailbreak
No GreenPois0n RC7 for iOS 4.3 But Shatter Exploit iOS 4.3 Untethered Jailbreak
RedSn0w 0.9.8b1 to Release Around 21th March for iOS 4.3 iPad, iPhone Untethered Jailbreak
GreenPois0n 4.3(RC7) and RedSn0w 0.9.8 Most Likely Release Date for Untethered 4.3 Jailbreak
RedSn0w 0.9.8b1 & GreenPois0n 4.3 Download for iOS 4.3 iPad 2, iPhone 4 Untethered Jailbreak