I also have had problems with the usb connection of my ipac. I was using an older board and purchase one of the new ones and both of them had problems when connected usb. They both worked fine using ps2.
Problem I was experiencing was that when connected to the usb, the actual controls (buttons, joysticks, etc) would the wrong keyboard "control" to the computer. Strange thing though, I could use the keyboard to play the games (still hooked through the ipac) and it would work fine. Only messed up when using the buttons and joysticks. Talked with andy a number of times and we never did resolve it (fixed by going back to ps2).
Note: What I said sounded like maybe the ipac was the problem, but I don't think so now. Think it was probably the computer, usb driver, xp,

??
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