I accidently upgraded through itunes (it wasn't jailbroken at the time), and now i want to rejailbreak it and unlock it, since i'm going on vacation and want to use the sim card i buy there.
I am not sure about the tool that you have specified.To jail-break you can visit Jailbreakiphone4sim.com and for unlocking the iPhone 3g you can avail the permanent remote unlock service from Classicunlocking.com and follow free unlock instructions from Mobileunlockguide.com