Download Jailbreak iOS 4.2.1 Using Redsn0w 0.9.6rc7 On Windows

Right click on the shortcut, select ‘Properties’ and go to the ‘Shortcut’ tab. Edit the command to reflect your current IPSW firmware. Replace ‘iPod4,1_4.2.1_8C418_Restore.ipsw’ to the exact name of your device’s firmware. Extract the Redsn0w 0.9.6rc7 zip file and copy Redsn0w.exe, the shortcut ‘boot-ipt4g’ and your iOS IPSW firmware to C drive.When you double click the shortcut, Redsn0w will automatically process the IPSW so that you don’t have to select it manually and select the ‘Just booth tethered now’ option (the –j argument in the command). So you are directly taken to the screen where you put your device in DFU mode.
All download links given at bottom.
The shortcut ‘boot-ipt4g’ points to the following command:

C:\redsn0w.exe -j -i “C:\iPod4,1_4.2.1_8C148_Restore.ipsw”

Download Jailbreak iOS 4.2.1 Using Redsn0w 0.9.6rc7 On Windows