[HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Control \ PriorityControl]

You will need to create a new DWORD: IRQ#Priority (where # is the number of the IRQ you want to prioritize) and give it a setting of 1. This setting gives the requisite IRQ channel priority over the other IRQs on a software level. This can be extremely important for functions and hardware subsystems that need real-time access to other parts of the system. There are several different subsystems that might benefit from this tweak. Generally, I recommend giving either the System CMOS or the video card priority. The System CMOS generally has an IRQ setting of 8, and giving it priority enhances the I/O performance of the system. Giving priority to the video card can increase frame rates and make AGP more effective.

You can give several IRQs priority, but I am not entirely certain how the system interacts when several IRQs are given priority – it may cause random instabilities in the system, although it is more likely that there's a parsing system built into Windows XP to handle such an occurrence. Either way, I would not recommend it.