Hi shateredsoul- I bought the same trackball from the same vendor and was also thinking the same thing as you are while I was waiting (configing ipac). As the listing says, it is a true plug and play USB. Once you plug it in your PC will recognize it as a mouse. You will then have access to the 3 buttons as left click/right click/ middle,(It doesn't come with them though ;-)) I got excited that Windows recognized it, but then I needed to configure MAME to reconize it. As of right now I am using MAMEUI and I went into config controllers section ( sorry I can't remember exactly what it says at the moment), and put a check mark where trackball is configurable. It worked......
I then wondered,what about the middle button??? what can I use it for??? since left and right buttons were working, so I recently tried out Missle Command and it worked no problems. So now I totally eliminated the mouse and just use the trackball to get around windows. Now if I could only figure out how to configure HYPERSPIN, it would be golden! Good luck