A couple of clarifications, no offense to Andy!
HeadRusch, there is a MAME32 version of MAME Analog+, checkout
http://www.urebelscum.speedhost.com/ (And no, USB has never allowed dual spinners with other than these versions of MAME.)
So this means that MAME Analog+ will be needed and Windows 98 as Microsoft don't recognise multiple mice in XP as separate devices.
Actually Windows 95 Release 2.1 (the one that supports USB), Windows 98, or Windows ME will work with either MAME Analog+ or MAME32 Analog+
Of course single player trackball and spinner will work with all OS and MAME versions with USB.
Actually, single PORT trackball and spinner will work with all OS and MAME versions with USB. (i.e. you can connect one t-ball and two spinners to the same opti-pac port and use any of them, but you need the OS and MAME Versions above for 2 trackballs or more than two spinners).
Correct me if I am wrong. . . (I am assuming the USB opti-pac uses the same switching as the previous one, but I don't know this. If it doesn't, you could still route everything through the first port and plug/unplug components as required.)