Nfs Underground 2 is a popular racing game that allows you to customize your car with various vinyls, decals, and paint jobs. However, if you want to use some custom vinyls that are not available in the game, you will need to download and install them manually. Here is a simple guide on how to do that.

1. Find a website that offers custom vinyls for Nfs Underground 2. Some examples are NFSCars, NFSAddons, and SoundCloud. Make sure to read the description and instructions carefully before downloading any files.
2. Download the vinyl file that you want to use. It should be a .zip or .rar archive that contains a VINYLS.BIN file and possibly some screenshots or readme files. The VINYLS.BIN file is the one that contains the actual vinyl data.
3. Extract the VINYLS.BIN file from the archive using a program like WinRAR or 7-Zip. You can also use Windows Explorer to open the archive and drag and drop the file to a folder.
4. Locate the folder where Nfs Underground 2 is installed on your computer. It should be something like C:\Program Files\EA Games\Need for Speed Underground 2 or C:\Program Files (x86)\EA Games\Need for Speed Underground 2 depending on your system.
5. Open the CARS folder inside the game folder and find the subfolder that corresponds to the car model that you want to apply the vinyl to. For example, if you want to use a custom vinyl for the Nissan Skyline, you should open the SKYLINE folder.
6. Make a backup copy of the original VINYLS.BIN file in case something goes wrong or you want to restore it later. You can do this by right-clicking on the file and selecting Copy, then right-clicking on an empty space in the folder and selecting Paste. Rename the copied file to something like VINYLS.BAK or VINYLS.OLD.
7. Copy and paste the downloaded VINYLS.BIN file into the same folder, replacing the original one. You may need to confirm that you want to overwrite the existing file.
8. Launch Nfs Underground 2 and select the car that you modified. Go to Customize > Vinyls and browse through the available options until you find the custom vinyl that you installed. It may be in a different category than the original one, such as Art Factory or Contest Winners. Apply it to your car and enjoy!

Note: Some custom vinyls may not work properly with certain car models or colors, so you may need to experiment with different combinations. Also, some custom vinyls may overwrite existing ones in the game, so you may lose some of the default options. To avoid this, you can use a tool like NFS TexEd to edit the VINYLS.BIN file and change the slot number of the custom vinyl.