I don't actually know how to disable the on-board graphics,. anyway i only installed Intel's HD graphics so i can run GPU-Z and EVGA's OC scanner regarding the OpenCL i think, and my games still use the GTX 570 regardless and so does other programs like YouTube/KMP player etc.
So everything is still all good.
Which do you use for a display? If you're using gtx570 then there is really no need for your Intel HD to be enabled. Unless you use a Quick Sync.
The GTX 570 of course, i was just wondering why device manager is acting the it was, nothing more than my curiosity