when you install windows 2000 with acpi enabled (default when your motherboard supports acpi) all pci cards will share irq's; you can't do anything about it. the reason you can't do anything about it has something to do with load balancing.
however i reinstalled win2k with acpi disabled (press f7 when asked if you have any additional controllers), so the pci cards won't share irq's. however it didn't solve the crackling noise problem.
you should also check your bios setting if you have a sb live; in that case you have to reserve irq5 for legacy device; worked out great for me.