The textures should somewhat resemble the preview picture. Red rocks, red sand, red cracked dirt, everything of the sort. They should be either 256x256, 512x512, or 1024x1024. They should tile (Check for tiling by doubling the dimensions and pasting 3 duplicates) and should appear seamless. If any of you live in New Mexico, this is an opportunity to go outside and take some pictures of the sand. Best if you can somehow get a large area, 128 inches across for 512x512, with a camera pointing straight down. So if you have a wide range camera THAT ISN'T FISH EYE, use it.
Formats: .PNG, .TGA, .DDS RGBA8888, .pdn, .xcf, any uncompressed format that can be opened in paint.NET or Gimp.