Found this over at The Inquirer... I did a huge enquiry into what you need to be DirectX 9 compliant after I saw some chit-chat, and possibly very important news, over at Reactor Critical.
That"s because some folks over yonder claimed that the new and upcoming Nvidia Geforce FX does not support displacement mapping --- a key element of Microsoft DirectX 9.
The guys and gals are right. Geforce FX does not have support for displacement mapping proposed by obscure little Matrox and implemented as a part of DirectX 9 but this still does not mean that Geforce FX is not DX 9 compliant, it emerged.
Knowledgeable sources now tell us that you simply don"t need Displacement mapping to be fully DirectX 9 compliant, and we also learned that Nvidia does support displacement mapping, although with some differences, you won"t be surprised to read.
This pretty much leads to the same situation that we saw with DirectX 8.1 and N patches support that were supported by ATI in its Radeon 8500 generations, while Nvidia didn"t support that specific implementation on its DirectX 8 compliant Geforce 3 and 4.