We did it
Firstly I upgraded with 6.0.1
with iTunes as 6.0 is not possible (make sure there's no address pointing out to saurik's server at the host file). After the Shift+restore with iOS 6.0.1 on iTunes has finished, the 3GS was doing "Searching.." At this point I didnt bother to go to activation, simply left it Locked.
After that I used "redsn0w_win_0.9.15b3" with administrator mode, and went straight to Jailbreak but I received an error " Missing keys.plist ". I closed the redsn0w, started it again directly to the jailbreak button and still received the same error.
Then I googled and found this "http://absinthejailbreak.com/forum/how-to-fix-missing-keys-plist-error-while-jailbreaking-ios-6-0-1/"
Then followed the instruction, and select IPSW to target to 6.0 , clicked "Back" and jailbroken my 3GS, make sure to check the install Cydia and Downgrade baseband. I could see the downgrading BaseBand process when the cute pineapple showed up. When its finished, I opened up redsn0w again and click the Just boot to get a tethered mode to install cydia.
When its finished, I could connect via wifi (my good friend's iPhone 4 hotspot, since It wouldnt connect via proxy ).
Although I reload several times, I still couldnt find the Ultrasn0w fixer (just ultrasn0w, so I added this : "http://repo.iparelhos.com" , please look into : "http://www.unlockboot.com/2012/10/unlock-ios-6-with-ultrasn0w-fixer-6.0.html"
After I installed the fixer first, I installed the ultrasn0w. That should do the trick
So glad, and thanks again guys. (sorry for bad writings, been celebrating with half a dozen good beers since LOL)