USB Lightgun with 2 mice?

[Afterburner]

I've got two trackballs that are recognized in XP as standard 3-button mice.

One is plugged into the PS2 port and the other is plugged into a USB port.

Both work just fine in mame.

I've tried to hook up the TopGun LCD Lightgun, but XP doesn't seem to want to recognize it.  I'm using the GunCon2 drivers.

If I unplug the 2nd trackball from the USB port, the lightgun works, both on the windows desktop as well as in mame.

What do I need to do to be able to use all three?

I'm using the lightgun and multimouse options in my mame.ini.

[u_rebelscum]

Without any more info, I'd guess it's power, or to be more precise, the lack of. 

One of the biggest problem with the TopGuns are they are power hogs, and AFAIK they need the full 500mA & 5 volts to work (and sometimes more than that at power on).  Are the TB & gun trying to share a USB hub?  Is the hub plugged into the wall (aka "self powered")?  Or, if they're not on a hub, are they on the same USB pair?  How about in the front of the computer?  Sometimes the pairs, more often if in front, are like an unpowered hub, and thus can't supply the full 500mA to both ports at the same time.

Things to try:
Plug into a wall powered usb hub.
Plug into two unpaired ports in the computer.
Plug the gun into a wall powered hub and the TB direct into computer.
Plug the gun directly into the back of the computer and the TB into a wall powered hub.
Try a different brand wall powered hub (one that can deliver higher than spec mA at power on).