Well I've been working with texture sizes for some time now... and it's really difficult to judge how large of a file morrowind can handle on xbox, since your not REALLY replacing the files, your just adding textures and thoes new textures override the old ones... so until we can figure out how to pack and unpack the xbox bsa file (the file that contains all the original data (textures, meshes, etc...)) we can't really make the textures the same size and the original xbox textures, as that would cause ddes... we actually need to add textures that are HALF the size of the Xbox textures, so an average land texture would come down to somewhere around 64x64pixels
if we could open the bsa, replace all the original textures with replacements, then pack the bsa again... im sure we could go at least 128x128 for a basic land texture, and twice that for bodies, faces, armor, etc...
By the way... theres an easy way to tell what size texture you will need... say an average body texture is 64x64... something smaller than the body itself would obviously be a smaller texture...
and one last note... the dds format needs to be pixel sized accordingly
1x.
2x.
4x.
8x.
16x.
32x.
64x.
128x.
256x.
etc...
the '.' represents one of the values to the left, so 64x256 would be acceptable....