You could setup a material effect and setup the filters in the texture to be linear in FX. Or if you know C++/native DirectX, you can setup your own vertices and polygons and render six 1024x1024 textures seperatly, making sure you turn off the Z-Buffer for rendering your skycube and turn it back on to render the rest of the scene.

Sorry I can't help you out on code but I hope I can explain it well to you.