Right you have two choices - play the slot shuffle, each slot has an irq - but it shares with something always... check your motherboard manual for what shares with what.

2nd choice, reinstall 2k and press f5 when it says press f6 to load scsi and choose standard hal. This will effectively tell win2k to bypass acpi and its attendant irq sharing. You will then be able to set irqs from the bios if the board allows it or 2k should then allow you to change the irqs for the devices.