IRQ 11 shouldn't be a problem (mine's on the same IRQ), but the fact that it's sharing it with the IDE controller might be. Are you sure the IDE controller wasn't using 14 or 15? My ide0 is on IRQ 14, and ide1 is on 15, and that's the way it's been on most systems I've seen...
Try looking at /proc/interrupts to see what's sharing what. If possible, load the modules for all the hardware other than the nVidia driver first, then load the nVidia one, to hopefully make it take its own IRQ. If that doesn't work, try loading the nVidia module first, and the others later.