To change the background image on your navmap you will need two things,
UTF editor
Custom 256x256 TGA image
The file you need to locate sits here, DATA\INTERFACE\NEURONET\NAVMAP\NEWNAVMAP\nav_prett ymap.3db
Open this up with the UTF editor, expand the tree and go down to the texture library section. There you will see the fancymap.tga texture and if you expand this, you will see the MIP0 section. This is where your new texture will go.
Create your new 256x256 image and save it as fancymap.tga. Then back to the UTF editor, IMPORT your new texture into the MIP0 section and save the file.
You should now have a new Navmap background
