Gaming cards are based mostly on DirectX support and cranking out pixels and geometry as fast as possible (faster clocks). The driver system is standard and more mainstream.
Workstation cards such as the NVidia Quadro series are based on pixel precision and geometry accuracy (perhaps slower clocking), a different driver system, and full open GL. They are for capacity in industries that use CADD, do professional video editing, and CG animation....... and usually offer more memory (512 MB). Using one of these for gaming will result in a very choked frame rate or no game play because most work cards are not usually based on DirectX and nor are they compatible.
Gaming cards are much less expensive than professional workstation cards and can do a good deal of 3-D and video editing work, but are not as accurate as workstation cards, and, as of now, do not usually have 512 MB of memory. Usually the maximum memory for a gamer card is 256.....but ATI is rolling out more bad boys!
If you do not build complex 3-D objects, do huge video editing or animations, and want to only game, watch TV, do small 3-D building and animation, and watch DVD movies, or streaming video, then a mainstream gamer card is your best bet.