There is a config.exe file (icon shown above) that comes with the game. For those of you who are not running Japanese Windows, the layout is as follows:
There are four large rectangular buttons going top down. These buttons are used to set the buttons for each of the four controllers. If you click on one of the buttons, you get the following screen
If you select one of these four large buttons, you will go into a sub-menu to set the buttons. On the bottom are three buttons marked Clear, OK, and Cancel. There is a smaller button to the right of the four main buttons in Figure 2. If you click on that button, you will see the following screen
that is used to test for response in case you wish to use the keyboard for multiple button response. Press ESC to exit this window. The game may not recognize more than one button push at a time so Figure 4 will show you the responsiveness of your setup. It is suggested that you use a Gravis GrIP Multiport, which you may be able to find on an online auction (the only problem is that there are no drivers for the GrIP for Windows XP). Another solution is to simply use a hub and plug in four USB gamepads. I currently use Microsoft Sidewinders (the gameport version).