Hi Bobford Sorry but not sure you can do what you want with a splitter. think your wanting to extend the desktop onto the 2nd monitor.
I'm not to familiar with NVidia cards as only use ATI Radeons at home try right clicking the desktop, select screen resolution it should then bring up your displays you should see a box saying Multiple displays click one of the screens and select "Extend desktop to this display"
That might work but as said not sure your splitter will allow you to do that. You will probably need either a 2nd graphics card or a new card with 2 ports either 1 x VGA and one DVI or 2 x DVI