I too managed to do some near 0 visibility on CATIII using 747, real weather settings in London and Italy. Apart from high beats per minute of the heart, and the engine sound, your instincts are the only one to help you think, that the ILS is showing you the right stuff, because many a time landing was done without having the required visibility at DH too.
Thats the good part of simulation, you think its fine, you carry on with the descent, and when you see that you are too low etc, you can restart and try all over again with a grin on your face!!! Imagine the real pilots plight.!! Thats the reason he is trained on ILS and needs to do it to perfection as compared to VFR.