Are you using the .DTX convert from BlackAngel? If so, then i'm not sure why you can't view the files.
Did you follow these steps? (Assuming you have .DTX Convert and dedit)
#1 - Extract the textures you want to mod from the .REZ file of your choice.
#2 - Place the extracted folder somewhere accessible such as your desktop and launch .DTX Convert.
#3 - For an individual file select (File -> Open File -> xxx.dtx) and for an entire folder select (File -> Open Folder -> xxx.dtx)
#4 - Click "Convert to LithTech"
#5 - Paste the converted .DTX files in your "Project" folder (or whatever you named it, and open dedit
#6 - Click on the textures tab and navigate to the texture you want to mod. Then right click it and export the file anywhere accessible.
#7 - Open up the newly exported .TGA file in Photoshop, Paint.net, or any other image editing application.
#8 - When you are done, save the modded texture as a .TGA
#9 - Open up dedit again and click on the Textures tab. Then right click and import the .TGA file you just modded.
#10 - Navigate to your "Project" folder (again, this might be something different depending on what you named it) and find your imported .DTX file.
#11 - Copy and paste, (because it's always good to have backups, especially with mods) the .DTX file somewhere accessible.
#12 - Open up .DTX Convert and select (File -> Open File -> xxx.DTX) and then click "Convert to Nexon"
#13 - You now have a modded texture that you can inject back into a .REZ file, or however else you bypass.