Super Street Fighter IV: Arcade Edition Setup:

Luckily Capcom® fixed the keyboard problem found in Street Fighter IV in Super Street Fighter IV: Arcade Edition(make sure you have the latest game patch). Simply be sure to have your X-Arcade plugged in before starting the game, then go to Options>Controller Setup and you will see at the top it says 'Keyboard 1'. If you press your keyboard's Right-Arrow key it should now say 'Keyboard 2'. Setup the player 1 side as Keyboard 1, and player side as Keyboard 2. Simply hit enter on your keyboard on the action you want to assign, and then press the button on the X-Arcade  that you wish to perform that action.

Street Fighter IV Setup:
Unfortunately Capcom® did not give much thought to the control options in Street Fighter IV for PC. For example, you cannot play with 2 players on one keyboard or a keyboard encoder like have been used in many brands of game controllers for many years. Also you can't use your custom keys on the Character Select screen. We recommend that you contact Capcom® to request that they release a patch to address these problems.

2-player X-Arcade Controller Setup :
Unfortunately Capcom® didn't allow you to play 2-players with one keyboard for controllers like the X-Arcade and many others that have been around for years. This means you will have to make one or both player sides of the X-Arcade emulate a game controller.

Option 1:
Make the X-Arcade emulate a emulate a game controller.

Option 2:
You can make the X-Arcade act like an Xbox 360 Gamepad. Simply unzip the file below  to your  Street Fighter IV installation directory (default: C:\Program Files\CAPCOM\STREETFIGHTERIV). You can edit the included x360kb.ini  to change keys used. There is also Tester included in it that you can use to verify your settings.

IMPORTANT: You must set the Button Config to default, and keyboard settings to none for all as shown below.

Download Here

If you have an error with the bracket keys (fierce kick on player 2 side), check your keyboard in Device Manager and make sure it is not listed as a MCIR 109 or 106 keyboard, if it is simply change the driver to  to "HID-Compliant device", or for a PS/2 keyboard "standard PS/2 101/102 Keyboard".

Thanks to DeLuSioNal29 for the heads-up on this one.

Solo X-Arcade Controller Setup:
When you first launch Street Fighter IV you will see a "Controller Settings" button on the launch menu, ignore this for the X-Arcade because the X-Arcade works as a keyboard not a game controller. Once you are in the game, go to "Start", "Options", then "Keyboard Settings". Here you can set up the game to use the keys for the X-Arcade's™ default Mode 1 button layout, or program the X-Arcade™ to use the keys that are default for the game.

Unfortunately you must use the arrow keys and Enter key to choose your character, so programming may be the best option for this.