External video cards are only for desktops.
The only way to get an external video card to work with a laptop is through the use of ViDock. http://www.villageinstruments.com/tiki-index.php?page=ViDock
Your laptop must have a ExpressCard slot in order for this solution to work. Many laptops do not have this slot. It seems to be phasing out of most laptop designs.