Modeling planets in 3dsmax is not difficult (I used to do a little), but unlike Photoshop, there you just wrap a texture around the planet, you can't play with the textures like you can in Photoshop. So, for Photoshop the only real thing you care about in a texture is the pattern, but if you want to texture in 3dsmax you need the finalized texture that would actually look good wrapped around a sphere and make a convincing planet.
So, you'd probably have to use Photoshop to create such a texture, then import into 3dsmax
Again though, that's unrelated to Sins, there was a thread about mod-modeling stuff by people more knowledgeable on how Sins treats it, I'm just talking basic functionality/differences of the two proggies
