Hi! I am new to this forums, so I don't really know what to do else.
That is silvermanblue's guide. So, I thank him for that. The problem is, whenever I tried to spawn the car, but when I opened my game, nothing popped out. I tried it to other cars (like Infernus) and it spawned, but not the added car. Please help I did this:
1. Extracted the downloaded files to San Andreas root directory.
2. I increased Vehicle Models = 212 to Vehicle Models = 213.
3. Placed the line VEYRON above BRAVURA line in handling.cfg
4. I added 16799, and the car's IDE line beside it.
5. In handling.cfg, I placed the handling line beside VEYRON.
6. In carcols.dat, I placed "veyron, <and its colors>" in alphabetically order.
7. (the optional step) In cargrp, I placed "veyron" in the group I wanted.
8. In hotkeys.lst, I made "0:16799
9. I placed "veyron" dff and txd files in gta3.img
What I also did is in HandlingAdder.ini file, I added 1 to [COUNT] (that makes 2), and placed 16799 below 411, below [CAR_IDs], duplicated 's code, renamed the duplicated  to .
I did not add any car audio or car name in-game.
All your help will be appreciated
Sorry, I did not duplicate the . I changed it to 16799, and below the [CAR_IDs] I changed 411 to 16799.