I have an 845 based board and let me share that the current design does NOT require spare IRQs, but the current direction is to do IRQ sharing. I only see an issue if someone tries to control the IRQs themselves.

Be sure the BIOS is current, that you've reset the CMOS confifuration data and avoid the slot next to the AGP slot and it works.

Of course, if you try to assign IRQs on your own, then that's your wrestling match. I can't help you.