they can be easily edited by right clicking, go to properties then go to change, then change it to a notepad file (.txt) Be sure to make backups of original files.

ok go to this folder (default destination) C:\Program Files\LucasArts\Indiana Jones and the Emperors Tomb\GameData\indy\gameinfo and locaste these files:
http://invis.free.anonymizer.com/http://www.geocities.com/taj_mesa_black/untitled.JPG)
(the ones crossed out cannot be edited

now right click on them
http://invis.free.anonymizer.com/http://www.geocities.com/taj_mesa_black/untitled1.JPG)
and choose Open With... (as shown above)

and open with NotePad...then the rest is explained in the files...the other thing that may be edited is the dialogue C:\Program Files\LucasArts\Indiana Jones and the Emperors Tomb\GameData\indy\dialogue all the .Txt files can be edited there to....change the text.....to adding new tips