Thus, to jailbreak your iPod touch 3G and 4G, you need to download iOS 4 firmware here:
download Limera1n by Geohot from this link. And the instructions to jailbreak your iPod touch 3G & 4G on iOS 4.1 can be found here.
Good luck guys!
Go to this page to jailbreak iPhone 3GS, 4 on iOS 4.1 using LimeRa1n for Windows