You need to install redsn0w onto your computer
http://blog.iphone-dev.org/post/1269...edsn0w-in-june

if you go and read my info thread in Computers, consoles & IT on here, named iPhone 3.0 and Jailbreak info... Loads of info and links there mate.

To unlock it, you'll need another program called ultrasn0w. That is found in cydia. Info in my thread again.

Watch vids on YouTube concerning the use of both redsn0w and ultrasn0w just so you get the jist of it before trying it