The .cdo and .cno files are the car models. The files you'll want to look into are the .cdp and .cnp files.
The layout of the files are as following:
Top of the file: Palettes
Bottom of the file: Textures
In TiledGGD, open one of the .cdp/.cnp files and you'll get the palettes/textures up, but you won't be able to properly see them just yet. The palette's should appear near the bottom right.
Use the arrow keys left/right to adjust the size of the picture. You can use the W key to adjust the resize amount aswell. Some files will have different sizes, so you'll need to experiment with the resizing to get a proper image.
Once you've got an image, let's make sure we get the correct format. Use the B key until the format says 4bits/pixel in the top right info box. Use P to change the palette order to BGR if it isn't.
To go through the palettes, use the Home and End keys to go through them. Home will go up, End will go down. You'll know when part of the cars textures is appearing correctly when the texture is in it's right colors. The first texture is always the tire rim, aswell as the first palette entry. You can then print screen and edit to your liking, then moving to the next palette.