The file you want is Ubisoft/SilentHunterIIIData/Textures/TLowRes/tex/druck_radio_7. You can paste any .tga picture you want on top of the picture in that file.
Or you can download any of the three folders full of already-done pictures from TikiGod at the bottom of this page:
http://www.subsim.com/radioroom/down...rt=date&page=2