IRQ (interrupt request) is a signal sent from a hardware device to the CPU to indicate that the device needs attention. Vista is a discontinued operating system from Microsoft. To check the IRQ of a device in Vista, you can use the Device Manager.
IRQs are important because they allow the CPU to prioritize which devices to service. For example, if a mouse and a keyboard are both connected to the computer, the CPU will typically give priority to the mouse, since it is more important for the user to be able to move the cursor than to type.