If i make a product (a 3D engine or game) using DirectX for commercial use, then do i have to pay Microsoft for using DirectX?

For using DirectX: no.

Read their licence agreement that came with the SDK as they are some legal clauses on how you should distribute the DirectX retail package; namely, the way you should include the DX installer on your CD and how you reference Microsoft''s web site and telephone support in any communication to your customers.

Also, you may want to get in touch with MSFT''s ISV Account Management staff for marketing opportunities, QA help, etc. You should also do the same with all the video card manufacturers you plan to fully support as they all provide support for driver debugging, optimizations, marketing opportunities, as well as freebies ...

Thanks buddy...

U mean i dont have to pay for using DirectX in my product but while distributing i only have to take care of the references to Microsoft. So, Microsoft is not charging on me using DirectX not on distributing my product with the directx runtime...
That''s nice

You can distribute your game without paying royalties to Microsoft for using DirectX.

But in order to ensure that your customers get the same DX runtime your game was designed with, you may opt to put the DX runtime on the CD along with your game. There are license clauses for covering this scenario and you need to provide the full runtime installer and make that clear in the documentation how this is made available.

If you document your game in a way that points to Microsoft for driver bugs and DirectX support, again Microsoft''s license agreement stipulates how this should be communicated to users(form, legal language, official contact points, etc).

Again, this is all documented in the DirectX SDK.