How to Use a PS3 Controller on a PC
All Credit goes to Jonathan, from Gamefront, for this!

1. Download MotioninJoy

Motion in Joy is a Chinese company that makes a relatively straightforward utility for using PS3 controllers with PCs. Your first step is to download their client from GameFronts fast, free servers.

MotioninJoy 32-bit Client
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MotioninJoy 64-bit Client
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2. Unzip and Install the program
The expanded archive will create an .exe file with the same filename. Run it.

3. Run DS3_tool and plug in your PS3 controller
When the installation completes, therell be a check-box prompting you to run DS3_tool, the Motion in Joy client. Leave it checked when you exit the installer. When the program opens, you should see this screen:

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When you plug in your PS3 controller to the USB port, Windows will recognize it, and begin installing drivers. This is misleading even though the installation completes, and the controller shows up in the Device Manager, it will not work.

4. Load the driver
From the screen pictured above, click on Load driver. At this point, Windows security will ask you to verify that you want to allow the driver installation process to continue. Since the new versions of Motion in Joy include signed drivers, this step is easier than it used to be. Assent to the installation and you should see a rapid series of messages in the DS3_tool window, pictured below:

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If you cant find the Load driver button, or you accidentally end up in a different part of the DS3_tool utility, click on Driver Manager to return.

5. Configure the controller
With the driver loaded, your next step will be to configure the controller for use. Click on the Profiles tab, pictured below. In order to take full advantage of the DualShock 3s twin analog sticks and many buttons, youll want to select Playstation 3, as shown in the picture. Once youve selected that setting, hit Enable, then Vibration testing. If youve followed these steps correctly, you should feel your controller vibrate. Motion in Joy also provides a convenient Game Controller Panel button, which whisks you directly you to the Windows controller calibration utility. You can use it to ensure that all of your controllers buttons are functioning correctly.

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6. Et voila! Enjoy gaming with your PC-connected PS3 Controller!
Some addition configuration and button-mapping may be required to get it working with your game of choice

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[Ed. Note: The below instructions do not work for Windows 7 machines]

One industrious modder out there has created a simple program so you can use your PS3s SIXAXIS controller on a PC like a game pad. Heres what youll need to do:

1. Download this archive and install the filter driver (libusb-win32-filter-bin-0.1.10.1.exe).
2. Unpack ps3sixaxis_en.exe
3. Plug the SIXAXIS into your PC.
4. Run ps3sixaxis_en.exe once.
5. Push the PS button on the SIXAXIS once if it doesnt see it straight away.