I built a DirectPad cable from a PSX extension cord, and am using it with a WinAmp joystick control plug-in.
I'm using a standard digital Sony PSX pad, no need for an external PSU. The I-Opener parallel port settings are, as far as I remember, at their default settings. The I-Opener is in the car, so I am not able to check right now.
DirectPad Pro requires certain files from the standard joyport driver to work correctly. If you have not already done so, have Windows install gameport support:
Start -> Settings -> Control Panel -> Add New Hardware -> Sound, Video, Game Controllers -> Microsoft -> Gameport Joystick.
Give that a try, then reconfigure the DirectPad driver.