Microsoft already released directx10 but only for WindowsVISTA since DirectX10 is built from ground up, on a totally different architecture. They started with a clean slate which means that more than half of the games and applications you used to run under XP with good old DirectX9 simply don’t work anymore with DirectX10 installed.
Directx is a collective name for a programming interface, Direct3D, Direct Draw, DirectSound etc, and is used to handle tasks in multimedia applications. Mainly used with video games, basically how well a video game looks.
If you want to fully utilize the power of directx10...you need to buy a new graphic card that support directx10 (as far as i know Nvidia 8800 series/ATI Radeon HD 2900 XT or higher) and obviously, you also need to buy a new OS "windowsVISTA" if your still using windowsXP. Oh and by the way...buy new games and applications that already support/utilize directx10. Sounds like we're going to spend a lot of cash just to catch up with directx10.
Here's some pictures taken from games regarding the difference of Dx9 and Dx10...
FLIGHT SIMULATOR X
AGE OF CONAN
Sample Videos from games:
CRYSIS with DirectX9 vs DirectX10
COMPANY OF HEROES with DirectX9 vs DirectX10
If you have windowsXP it stops at DirectX9.0c. DirectX10 is NOT backwards compatible as they claim at Microsoft. People call it "artificially" backwards compatible which means it will only "emulate" DirectX9, but that’s not the real step back since it’s built on a totally different architecture.
It will take years for most gamers to catch up and take advantage of DirectX10 since Microsoft excluded XP and Xbox360. Bad move for their marketing strategy and I hope Microsoft will realize that they needs to work on the backward compatibility issue since its a big deal especially with end-users.
Here's some benchmark from the game ‘Lost Planet’ DirectX9 vs DirectX10
More info about DirectX10
There is an on-going project for DirectX10 to run on WindowsXP which is called ALKY PROJECT by an independent group. Its already on ALPHA version and it is said to be working for some users. So if this group pull this one out for XP, then we can use those money to upgrade videocard instead of buying a new Operating System...hahaha!
About DirectX11, Microsoft will release it for Windows7...hopefully this one will have better review when it comes to backward compatibility. For more info about DirectX11, click here.