How to create large planet for space sim background?

Hi guys,

I'm trying to create a skybox that contains a large planet in it like this: http://www.youtube.com/watch?v=nQpOgAA21oE&feature=related

I made a skybox in Spacescape and tried to place a large planet object in there as well but when I imported the six images into the Skybox material slots, the planet edges didn't line up correctly.

Any ideas on how this process works?

Thanks, nanotec33