It all depends on your motherboard. Due to the lack of physical IRQ's in a system, most motherboard manufacturer's hardwire the USB bus to share an IRQ with something, but it usually the PS2 IRQ.
Take a look at the documentation for the motherboard. They almost always show how and where the hardwired IRQ's are. Then it is matter of rearranging the boards to not share.
You can also free up IRQ's for devices you are not using. For intance, the COM and LPT ports. If you are not using these, then you can free the IRQ's and (again, depending on the motherboard) use them for other devices.
There is not magic solution to this. Every motherboard is different. The basic rules are this:
1) Remove Windows drivers for any device you are moving or going to remove BEFORE you do it.
2) Check with the motherboard docs to see how the physical IRQ's are assigned to the slots and what else they share with (PCI Slot 1 is almost always shared with the AGP bus,..never put a card in PCI slot 1).
Good luck.
