USB Optical mouse causing POST to loop

I just about have my KT7A (non-RAID) up and running smoothly except for the glitch mentioned in the subject line.

When I have the MS optical Intellimouse connected to the PS2 port the system boots up normally; when I try it in a USB port, the POST sequence refuses to complete and loops indefinently. Any ideas of how I can fix this?

Of note is that my UPS uses USB to communicate with the system, and it runs fine. However, that function is controlled through Window98 SE, and W2K Pro (the system is dual boot).

My PCI slots are populated as follows:

1. none (using Hercules Prophet II Ultra in AGP slot)
2. Adaptec 19160 SCSI controller
3. USR Performance Pro modem
4. Intel NIC
5. Santa Cruz soundcard (needs to be here to avoid IRQ conflicts)
6. Mylex AcceleRAID 170 SCSI controller

I am using the YH BIOS, and 4.29 (final) 4in1 drivers.