I'll tell you that How to Jailbreak and Unlock Your ipod or iPhone 3G Using RedSn0w (Windows)
[4.2.1]...
These are instructions on how to jailbreak your iPhone 3G on the 4.2.1 firmware using RedSn0w for Windows...
IMPORTANT FOR UNLOCKERS
During this process you can update your baseband to the 06.15 version. If you are on 05.14 or
05.15 or higher you will need to do this to unlock. You do not need to do this for jailbreak only.
Please read the following very carefully before deciding whether to do this.
1. There is no way to come back down from 06.15, and there's no hiding the baseband version
from Apple. You'll be voiding your warranty in a very obvious way.
2. If some future baseband comes out with a critical fix, you won't be able to update to it if it
remains down in the 05.xx sequence (then again, you wouldn't update to it if you wanted to keep
your unlock anyway).
3. Starting with FW 4.2.1 if you have 06.15 on your iPhone you won't ever be able to restore to
stock firmware (it will fail). You'll need to only restore to custom IPSWs (then again, if you're
unlocker you should already be doing that).
4. There are reports that 06.15 may disable your GPS. The iPhone Dev-Team is currently
working on a fix.
Don't update to 06.15 if you don't need to! Only do this if you need the unlock and you're stuck
on 05.14 or 05.15, and you're willing to assume the above risks.
Iphone or ipod jailbreak is very easy if you are doing well otherwise it's so tuff for newbies. But don't worry I just wrote a guide who tell full jailbreaking with screen shoot..
