This first windows tutorial from modmyi.com and the mac version is from iclarified. Credit goes to them for the tutorials. The mac tutorial is on the bottom so keep scrolling down until you see it.

How to Jailbreak Your iPhone 3G on OS 3.1.x Using RedSn0w (Windows)

This is HOW TO JAILBREAK iPhone 3G 3.1 on windows! (XP,VISTA,7)

Before you start you need to have the following:
1. a copy of itunes 8.2 if you don’t already have it installed. (download it here Itunes 8.2 Link
2. a copy of custom firmware

3.1. You can get one from Our Custom Ipsw’s Downloads Page
3. a copy of Redsnow 0.8 (download it here Redsnow 0.8 Link
4. a copy of the OFFICIAL 3.0 firmware. You can get it from Our Official Ipsw’s Page

*If you currently have your iphone jailbroken at the 3.0 level, put your phone in RECOVERY Mode (not DFU) and use steps 1,2,3,14 & 15

**If you currently have your iphone at an OFFICIAL 3.1 level, complete all of the steps.

Step 01: If you have Itunes 9 installed then uninstall it.

Step 02: Install Itunes 8.2

Step 03: Run Itunes 8.2

Step 04: if you get an “itunes library.itl” error then delete or move it from your itunes folder in “my music”

Step 05: Once you have iTunes 8.2 running, put your phone into DFU mode

Step 06: click “ok” when itunes tells you it detects your phone in recovery mode

Step 07: once your phone is in DFU mode, hold your shift key and click restore in itunes

Step 08: a window will open and you will now locate the official 3.0 firmware file and select it

Step 09: itunes will now install the official 3.0 firmware onto the phone

Step 10: at the end of this process you will likely get a error 1015 or something like that. ignore the error by clicking ok and your iphone should be showing the usb and itunes logo at this point.

Step 11: Now open up Redsnow 0.8

Step 12: Browse for the 3.0 official firmware and follow the directions that the software gives to jailbreak the iphone. during the jailbreak process for 3.0, you will notice that it seems to freeze at the “installing activation bundles” part. Don’t worry, it is not frozen. Just give it a little while and it will finish.

Step 13: At this point your phone might have the USB and Itunes image back on it. This is fine. Open iTunes back up and you will probably be greeted with the “itunes detects your phone in recovery mode”. Click OK.
DO NOT PUT THE IPHONE IN “DFU” MODE AT THIS POINT. Leave it in “Recovery Mode”. Leave it as it is.

Step 14: Once again, shift click the itunes restore button and select the 3.1 custom firmware.

Step 15: THAT’S IT! Let it load the 3.1 custom firmware and you are set!

I have done this on 3 3G iPhones and can confirm that this process absolutely works. I hope this helps all of you that have been waiting on a windows version of redsnow that jailbreaks 3.1. This process may take more time but it will work.

Just to clarify a few steps in this process…

If you are on official 3.1 firmware, you have to downgrade to a jailbroken 3.0 firmware and have iTunes 8.2 installed in order to restore the CUSTOM 3.1 firmware. If you are already on a 3.0 jailbroken firmware then just make sure you have iTunes 8.2 installed because itunes 9 will give you error 16xx messages when you do a restore for CUSTOM 3.1 firmware.

I noticed that the majority of my steps look as though this is just to jailbreak to 3.0 SO i just wanted to make it clear that this is actually instructions to jailbreak 3.1

How to Jailbreak Your iPhone 3G on OS 3.1.x Using PwnageTool (Mac)

This tutorial will show you how to jailbreak your 3G iPhone by creating a custom ipsw that can automatically jailbreak, install applications, and add your own boot logos.

To learn how to use PwnageTool to unlock/jailbreak a 2G iPhone you can use the tutorial which is here

Step One
Make a folder called “Pwnage” on the desktop. In it, you will need a couple of things. PwnageTool 3.1, found here or here

You will also need the 3.1 iPhone firmware.
3.1.0 (3G): iPhone1,2_3.1_7C144_Restore.ipsw

When downloading the IPSW file, it is best to download it with Firefox since Safari often auto extracts it!

Step Two
Double click to mount PwnageTool 3.1 then drag the PwnageTool icon into the Pwnage folder.

Then from the Pwnage folder double click to launch the PwnageTool application.

Click Ok if presented with a warning.

Step Three
Click to select Expert Mode from the top menu bar

Step Four
Click to select your iPhone. A check-mark will appear over the image of the phone.

Step Five
Click the blue arrow button to continue. You will be brought to the “Browse for IPSW” page. On my laptop, it automatically found the IPSW. If PwnageTool doesn’t automatically find the ipsw file you can click Browse for IPSW….

Click to select the found IPSW file, a checkmark will appear next to it. Then click the blue arrow button to continue.

Step Six
You will then be brought to a menu with 7 choices. Click to select General then click the blue arrow button.

The General settings allows you to decide the partition size. Check Activate the phone if you are not with an official carrier then click the blue arrow button.

NOTE*: Deselect Activate if you have an iPhone legitimately activated on an official carrier.
NOTE*: You may need to increase the size of the root partition slightly. My first attempt failed at creating the IPSW until I increased the size to about 695 MB.

The Bootneuter settings are greyed out for the 3G iPhone. Click the blue arrow button.

The Cydia settings menu allows you to create custom packages so you do not have to manually install the necessary them later.

Click to select the Download packages tab. Then click the Refresh button to display all the available packages. Double clicking the package you want will download it and make it available in the Select Packages tab.

Checkmark the ones you want then Click the blue arrow button.

The Custom Packages Settings menu displays listed package settings for your custom IPSW. For know leave these settings as is. Click the blue arrow button to continue.

The Custom Logos Settings menu allows you to add your own images as boot logos. Click the Browse button to select your Boot logo and Recovery logo. If you would like to use the iClarified ones they can be found here: Boot Logo, Recovery Logo

Remember the rules for them: RGB or Grayscale format with Alpha channel and dimension bellow 320×480…

Click the blue arrow button to continue.

Step Seven
You are now ready to begin the pwnage process! Click the Build button to select it then click the Blue arrow button to begin.

Step Eight
You will be asked to save your custom .ipsw file. Save it to your Pwnage folder you created on your Desktop.

Your IPSW is not being built. Please allow up to 10 minutes.

You will be asked to enter your administrator password. Do this then click the OK button.

When prompted if your iPhone has been Pwned before, we clicked No. It allows for a more thorough restore.

You will be asked to turn off the device. Make sure it is connected to the USB port.

Step Nine
Be ready to follow directions now. It will ask you to hold the home button and the power button for 10 seconds. Then, you will have to release the power button and hold the home button for 10 seconds to enter DFU.

If you fail, it will show you a message. Click Yes. Unplug the iPhone from the USB. Turn it off, then turn it back on. Plug it back into the USB and turn off the iPhone when prompted.

When done correctly, PwnageTool will display a message telling your that it successfully entered DFU mode. iTunes will also pop-up.

Step Ten
In iTunes, hold the Alt/Option key and click Restore.

Step Eleven
Navigate to the Pwnage folder on your desktop using the dialog window that appears. Select the custom IPSW that was created (iPhone1,2_3.1_7C144_Custom_Restore.ipsw) and click the Open button.

Step Twelve
iTunes will now restore the firmware on your iPhone. This can also take up to 10 minutes.

If you so desire you may restore from a previous backup to keep all your settings or set your iPhone up fresh.

Step Thirteen
Once the restore is completed your iPhone will reboot and you will notice Cydia is present on the SpringBoard!