Dedicated video cards - I guess this is about dedicated video RAM.
Many laptops use so-called "shared" memory: the graphics subsystem doesn't have its own dedicated memory, instead it uses some of the main memory. 
The disadvantage of shared memory is reduced performance - the route between the graphics processor and main memory is a lot slower than the route between a graphics chip and dedicated video memory.

Shared memory is not as commonplace in desktop computers. Cheap desktop computers sometimes have "integraded" video - a graphics chip mounted on the mainboard, which often uses shared memory. 
But each and every desktop computer that uses a graphics expansion card will have dedicated graphics memory - it's mounted on the expansion board.

You'll probably want to avoid systems with "integrated video" and/or "shared video memory".

When it comes to rendering, the speed of the graphics subsystem is a non-issue. Rendering is done using the CPU only. So if you plan on building a machine that will only render, you'd best spend your money on a fast CPU and use the cheapest and simplest graphics system you can find.
But when it comes to setting up a scene, graphics performance is much, much more important. If you plan on building a PC for building 3D scenes, you'll want a fairly fast CPU and a very fast graphics subsystem.

I build my Vue scenes on an Athlon64x2 4400+ system with an nVidia 7800GTX graphics card  (512 MB dedicated graphics memory) and 4 GB of main memory. Works fine and fast. The machine is a year old, so by now there are faster machines, and faster graphics, but when I bought it, it was definitely a high end PC in all respects.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

My gallery   My freestuff