The textures of the car need to be in the TGA file format. This format is like BMP, but it allows 32-bit color (24-bit with 8-bit alpha). If they are already in TGA format, no need to worry. If they are not, you need to use a program like Adobe Photoshop, The GIMP, or paint.net.
Now, open a command prompt, and type in mktex *.tga *.tex /a
That will turn everything with a TGA into a TEX.
NOTE: If you are using the tintpack, Do not put the tintpack's TEX file in the folder until after you have done this.
If you converted the car from Need For Speed, use /t instead of /a.
Once you are done reading all this, you can move ONWARD.