I believe redsn0w works on the 3G. Might be a beta version that supports 4.1, can't remember. Limera1n and greenposion will not work for 3G regardless of firmware version because they use an exploit specific to the A4 in newer devices
I downloaded and am attempting to jailbreak with redsn0w 0.9.6b1 on windows. It starts the process and displays "uploading ramdisk" and the phone shows "downloading jailbreak data"
But it get's to 2 bars on the progress indicator and never finishes
You're sure it's on 4.1? The exact same thing happened to me, I tried Redsn0w to jb 3.1.3 but I actually was on 4.0.1 (didn't downgrade properly the first time). I restored properly to 3.1.3 then did Redsn0w again and it worked.
Ah, would've helped if I couldve seen what machine you're running on lol. Yes, that is indeed a common problem with Windows 7. Especially the 64-bit. XP and Vista usually do fine. Glad you got it worked out.