Can I jailbreak my 3gs? HELP

[markymark5434]

I have a 3gs on 4.0.1 currently jailbroken, that I did with the jailbreakme website a while ago. I used f0recast to determine my bootloader version as 6.4
However, now, I want to have a jailbroken 4.2.1.
I'm not sure if I can, with the new/old bootrom deal and all... I don't want to have a tethered jailbreak - its seems to much of a nuisance.
So does anybody now how I can go about jailbreaking it this time? Will it be untethered? Which program do you recommend using? (I am using Windows 7)

Thanks
(Oh and I have tried googling this excessively, and I still can't figure out if I'm good to go)

 

[noiceT]

Have you checked the dev team page?
Should have all the info you need.

http://blog.iphone-dev.org/

 

[mikelegacy]

6.4 is EASILY the new bootloarder, as the old bootloader is anything 3.5.3 or under. Also, an easy way to tell is if your 3GS was made BEFORE the 40th week of production, you usual always have the old bootloader. And if you upgrade to 4.2.1, you will NOT have an untethered jailbreak, as it's not released yet. Stay on 4.0.1. You aren't losing anything major. Just airplay really.