blackra1n jailbreak...HELP! [windows]

[zalalak]

Hey everyone,

I recently just bought a brand new white iPhone 3GS from AT&T but i have t-mobile. I thought i would be able to unlock & jailbreak it easily because before, i jailbroke 3 2g & a 3g but on the 3.0 firmware.
I tried jailbreaking my 3gs with blackra1n but the geohot picture never showed on my iphone & it would always get stuck on the reboot so i would have to force to reboot the iphone & so it is unable to jailbreak. my iphone has the 3.1.2 firware

What can i do?
&is there an alternative to jailbreaking/unlocking with blackra1n?
please help if you can
THanks(:

[HIMklg]

This should help.. it's definately the best video out.. [ame]http://www.youtube.com/watch?v=u7DnqOS1njU&NR=1[/ame]