Under Windows XP, you can use MameAnalog+ version .74 through .83 to access multiple mice in Mame.
Also, newer versions of AdvanceMame has the option to use multiple mice in WIndows XP.
Your best bet is going to be to wait for the next Mame version to come out which will support multiple mice (as Peale suggested). You could also compile your own 104u5 if you wanted, and in that case you should be ready to play.