Imagine if the forum resorted to "Help me!" subjects only? Take a moment to use that to help a forum poster to see that and think "I know that issue."
"I need to buy a good graphic card for it so that can display all programs (including 3D games) very well."
That's simple. You'll want the top to top 3 cards offered by Nvidia or ATI. There are the players today.
BUT let me comment that "all programs" can be a problem. Some gamers lament that one game ran best with some extra version of DirectX and some version of the video driver and had to install another DX and driver for best performance in another game.
There is no cure for that one.
In closing, my advice today is to not overexpend on 32-bit only machines. The writing is on the wall and you may be upset if 64-bit arrives and you spent too much on last years model.
I am going to buy a new computer for myself. Its parts will have high performance.
I need to buy a good graphic card for it so that can display all programs (including 3D games) very well.
Which standards (such as DIRECTX 9.0) is more necessary than others for graphic card to operate very well ?