This is one thing i'm not entirely sure on so i'll ask advice before fiddling with the GW.dat file
Firstly i'm not sure how/if its possible to browse the files in a .dat and secondly would it be possible to export some of the textures the games maps and terrain use. This of course is also dependant on the filetypes they use and wether they come in image files or .dds files
Textures
Raaaaa