Your onboard should automatically disable when you install the new card. You will need to install drivers for the new card once it is installed.
Static can kill numerous pc parts but mainly memory is in most danger, a video card would take a major static hit to kill it, just ground yourself on a metal part of the case before touching anything inside.
Wear cotton type (non static creating) clothing when you do this install, ground yourself to the case by touching it on a metal part, best not to work standing on carpet, work on a non conductive bench.
SLi is using mutliple nvidia graphics cards on a nvidia chipset board, Crossfire is using multiple ATi cards on an Intel chipset board