I believe that's .tga for the item images. I maybe wrong. I'm new to modding.
I'm not sure myself, it has been a few years since I touched the CS. My brother doesn't have a CS disc so I had to track a download of it down so I can figure what files are what.
Edit: Okay, you are correct about the file names, so I'll just make a random weapon and give the program you recommended a test.