Here is a patch for to get cpqphp working with IOAPIC.
My earlier statement that a kernel patch is not needed for 2.6 is
true only when ACPI is enabled.  A similar patch is needed in
pcibios_enable_irq() for 2.4 kernel and I will send it out
later.

The fix is in pirq_enable_irq().  This function is called indirectly
by pci_enable_device().  For device present during boot up, it should
get the proper dev->irq for pcibios_fixup_irqs() has been called to
get the dev->irq from MP table. If the value is still zero, then
this is properly caused by "buggy MP table".  For hot-plug device,
its dev->irq is 0 when the pci_enable_device() is called for it hasn't
gone through the fixup.  Therefore, the code (similiar to the code
in pcibios_fixup_irqs) is needed here.