Here is a guide from sleepers

Well it’s still not available for Windows users officially, but what you can do is follow these instructions and load the pre-built custom firmware image. You will have to download the image from a torrent. The details are able to be found here.

Unlock via Custom Firmware for Windows

Step 1: Use WinPWN 1.0 To PWN Your 1.1.4 iPhone. If you need WinPWN Get it: http://www.winpwn.com/files/winpwn_1.0.0.3_RC1_Setup.zip
Step 2: Install BootNeuter (Available Via Installer).
Step 3: Run BootNeuter and have it Neuter your iphone
Step 4: Make sure your iTunes version is at 7.7
Step 5: Grab a pre-created IPSW Made with PWNAGE 2.0 Mac. If you dont have one made you can grab one here: http://thepiratebay.org/tor/4305453/iThor__s_iPhone_2.0_Custom_Firmware_Vanilla_(5A347)
Step 6:Put your phone into recovery or DFU mode.
Step 7: In iTunes Shif+Click the Restore button and find your custom IPSW Firmware file.
Step 8: Wait for it to complete! ENJOY!

Regards

Anil Chopra