Hmm, for once wiki has gone into lots of detail, it confused me a bit.
How i think of IRQ's is like they are addresses or stations along the bus line. Each hardware device is assigned to one of these addresses/stations and that is where it resides. IRQ errors can come when one or more devices are assigned to the same address and are calling memory references at the same time.
To see your systems IRQ's go to START - RUN - type "msinfo32" and then scroll down a bit to find the part about IRQ's.