Need Help - Jailbreaking and Unlocking iphone 3G on 4.2.1. w/ Windows

[jrhino]

I have a friends iPhone 3G that was jailbroken and unlocked for T-Mobile, but she sync'd it and upgraded to itunes (yeah, I know - sigh). It upgraded the phone to 4.2.1. Can you provide me with the steps I need to jailbreak and unlock the phone again? Oh and BTW - I am a windows user.

Thanks in Advance!
JRHINO

[Simon]

Firstly download f0recast to see if it has a 5.8 bootloader or not.