Can I disable Nvidia card and use onboard video?

Even then, removable graphics does not necessarily mean you can upgrade or downgrade. It means it is easier for Dell to replace specific parts if needed.

However I can tell you one thing. The only way to switch between integrated and dedicated cards on a notebook that does not come with Optimus (or similar) technology in the box...will require a new motherboard (if possible at all).

 

You have an 8600M GT that is removable, and uses a proprietary slot design, and you have options such as the 8400M GS and 8600M which you already have.



You cannot use onboard video as the Vostro 1500 does not have switchable graphics; neither do you have an X3100.

You either buy a new 8600M from ebay, or purchase a new notebook. I'd recommend the latter.