AFAIK, Windows NT, 2000 and XP can assign IRQ's above 15 if the
motherboard is equipped with multi-processors, i.e., 2 or more and the
HAL is for multi-processor. OTOH, the current breed of hyperthreading
(HT) CPU's may substitute for multi-processors. IRQ numbers above
15 are supposedly to be "virtual" lines versus physical IRQ lines allocated
for 15 and below.