In Windows, there is typically 4 types of rendering methods available to programmers: Glide,OpenGL, Software and DirectX. In Linux, glide and OpenGL are primarily used.  These are the ways that 3D graphics are shown on video cards.  The fastest is Glide, which was developed by 3DFX, but is no longer endorsed as 3DFX is now bankrupt and NVidia isn't going to endorse it since it doesn't support Hardware T&L.   

The idea behind these methods is to attempt to get the video card to render as much of the scene as possible to help free up the limited processor bandwidth which could be used instead to make the game even faster.  This is the reason that Graphics cards are using increasing faster CPU's, to be able to render more then ever.  While this idea sounds simplistic, the companies have to worry about costs.  Also, with the CPU war warming up, CPU's are so fast they dont really need fast video cards to render stuff and can render everything anyway.  However, Hardware T&L now has many advantages that even processors dont have. 

With Hardware T&L (transform and lighting), video cards such as the Geforce series are capable of rendering scenes with ultra-realistic graphics.   THe graphics themselves are composed of millions of polygons.  The less polygons in a scene, the more blocky it is.  The reason Transform and lighting is helpful is that suddenly, the video card can render the lighting instead of leaving it to the cPU.  TRaditionally, lighting takes alot of processing (especially raytraced lighting which is lighting which creates sharp shadows).  Unfortunately, raytraced lighting is neccessary for high quality graphics.  OpenGL and Direct3D are the only rendering methods which support Hardware T&L.  Hardware T&L is the future and is a neccesity for speed now.

Another promising technology that was developed by 3DFX was T-buffering which offers Motion blurring and many other advanced features.. Nvidia will probably incorporate T-buffering into their software in the future.

Anti-aliasing is simply where the 3D acceleration averages out the pixels around different objects to make the scene more realistic.  FSAA (Full-scene Anti-aliasing) is simply an improvement of this technology.

There are many features on video cards but I am only improving your awareness of some features... If you want to purchase a card, buy one which is AGP (a small single slot in most computers that is dedicated to graphics and allows textures to be transfered directly to the card.  1X is good enough, but the higher speed, the better) and one that offers t&L.  ALSO dont get any 3DFX cards or your card wont work in later versions of Windows, but fortunately, will for linux.