sorry I have wrong the reply
from http://www.musicxp.net
"The number of available interrupts is increased from 15 (0 to 15 with irq2 reserved) to 24 or more with an APIC system, when using XP and ACPI.
Indeed, some IOAPIC's have 64 interrupts, and some motherboards have more than one APIC, potentially giving hundreds of IRQ's.
You should find that there is absolutely no IRQ sharing whatsoever when using an APIC/XP/ACPI installation."