There are two patches: one is a backport of the official DX11 done by a Russian team (the same team that backported DX10), the other one is a wrapper for OpenGl. The thing is that the backported version has never been finished and it has a very limited compatibility with games. Besides, the Russian team that was working on it dropped the project. As result, @Svyatpro and others ported the Linux implementation to XP: on Linux DX10/11 games go through a wrapper which translates the calls to OpenGl, executes them with the GPU and then it translates it back. Although OpenGl is a fairly good protocol and the translated calcs are "just" Single Precision Floating Point which are perfectly handled by the GPU (both AMD and NVIDIA) due to the large number of 32bit capable units in consumer GPUs (there are a lot of single precision units and half precision units in consumer GPUs and just a few double precision units), unfortunately translating calls back and forth slows the whole thing down.
In other words: does it work? Sort of. What do I do if it doesn't? Either help the project yourself or nothing.
My memory might not be perfect, though, but I'm pretty sure this was the situation 'till a few years ago, before people started forgetting about it.
P.s I don't play games; last time I did was many years ago and I've never been a gamer; the only reason why I use a GPU (other than display a video) is to use OpenCl to speed up Discrete Cosine Transform and Fourier Transform calculations. In other words, I couldn't care less if the latest DX prevents a game from running on XP as I wouldn't be playing it anyway...