There is a quick "hack" way, make your favorite picture into a DDS file, using a converter...
Get a file converter program off the internet, step 1
Also, if you are making a texture for an existing ship, use the original texture files as a template, using the existing configuration to plan out where and how your textures should go.
(yes, I have no proper program, XSI mod tool crashes my computer
Autodesk is the wrong format, others are exotic unworkable formats, etc
You could try changing the pointers on the Mesh to point to different files, I made a nice New York Planet from a New York city map, also used a Borg wallpaper for a nice Uber-City Planet

(the planets are easy, the ships are a lot harder to match up edges)
I'm sure the next responder will tell you which programs will do it properly...