This is a graphical addon that I use with my base Orbiter installation. It improves the graphical rendering quality of the program tremendously and is highly recommended. It is currently under development and as of this writing the current version is RC44, you can get it here. The D3D9Client is compatible with Windows XP (as well as Vista/7) and works with most video cards. However, if you have a DirectX 10/11 compatible video card and are in Windows Vista/7, then you can use the D3D11Client instead, you can get this one here.