So if you wan to unthetered jailbreak iOS 5.1.1 on iPhone 4S, iPhone 4, 3GS, iPad and iPod Touch using Absinthe 2.0.x for Windows, then follow the instructions below.
FYI: if you are Mac user, can jailbreak unthetered iOS 5.1.1 here.
Step 1: Download and then extract the Absinthe -- the latest one. And then doublec-click on the absinthe-win-2.0.exe within the folder you previously extracted.
Step 2: After you double-clicked on the .exe file, a folder namely absinthe-win-2.0 will be created.
Step 3: Now within the folder, click on the absinthe.exe file
Step 4: When prompted, plug your device to your PC using USB. Be sure all passcodes or VPN settings are removed first.
Step 5: Now click on the Jailbreak button to begin the jailbreak.
Step 6: Absinthe will begin jailbreaking by going through several steps like beginning jailbreak, sending initial jailbreak data, waiting for reboot and then completing process. Just wait. Till you find this message.
Step 7: Now you should see a Cydia icon appears on your iPhone's homescreen. Which means your iOS 5.1.1 is jailbroken now!
That's how to untethered jailbreak iOS 5.1.1 on iPhone, iPad, iPod touch for Windows using Absinthe 2.0.