So, you've downloaded, unzipped/rared/whatevered a mod. In MOST cases, you'll have a DFF, a TXD, and a readme file. It's strongly recommended you read the readme, as they usually contain important information about the vehicle, like known bugs, extra steps for installing, etc.
First, the number one problem people have when installing mods is that the files are read-only, meaning they can't be modified. Right click on your Vice folder, click on Properties, UNcheck "read-only" in the box that comes up, then click OK. If another box comes up, make sure to select "Apply to all subfolders and files", then click OK.
Now, browse to wherever you installed GTA3/Vice City. There will be a folder called 'Models'. Open it. There should be a file named GTA3.IMG. This will be the same for both games. Open it with the IMG TOOL (Click for download location).
Take note of the filenames of the DFF and TXD files that the mod contains. For this example, lets say they are called 'banshee.dff', and 'banshee.txd'. This means they would replace the Banshee. So, in the IMG Tool, go to 'Edit', 'Search'. Type in the name of the vehicle it would replace, eg "banshee".
You'll get two results. Rename (Commands - Rename) them both to "banshee-old". Then Add (Commands - Add) the DFF and TXDs that you downloaded. Once they are inserted, rebuild the archive (Commands - Rebuild Archive).
IF your game has a file called TXD.IMG, delete it, and its sister file "TXD.DIR". Don't worry, the game will rebuild it on the next start up.
Now, the mod will work at this point, however, the wheels probably aren't going to look very good, and the handling will stay unchanged.
Most cars use D-Magic's Wheel Mod (Click for download location). Make sure you have that installed, though thats beyond the scope of this article.
Refer back to the readme. Most will have two lines of code, similar to the ones below somewhere in them.
| BANSHEE 1400.0 2.3 4.5 1.6 0.0 0.0 -0.25 70 1.10 0.84 0.53 5 200.0 33.0 R P 11.1 0.52 0 34.0 1.8 0.18 0.30 0.49 45000 0.25 -0.18 0.5 0.3 8183 1 1|
| 159, banshee, banshee, car, BANSHEE, BANSHEE, null, executive, 10, 7, 0, 237, 0.7|
The first one is the handling information, the second is the main definition for the vehicle. So, highlight and copy the first one, browse to 'Data' and open up 'handling.cfg' with Notepad (or any other PLAIN-TEXT editor, MSWord not recommended). Search (CTRL-F) for 'banshee". You'll find a line with the word 'banshee' at the start, and a whole heap of numbers after it. Highlight the entire line, and paste the line from the readme over it, making sure no other lines are disturbed. Save that file.
Now open up default.ide. Do the same thing. If the readme only mentions wheel size, find the line for your vehicle, and look at the very last number. Change it to whatever the readme says. Save this file too.
Now, start Vice, and your installed vehicle should work perfectly.
If you still have any problems, THEN start a new topic.
Also, I'd like to thank Victim of a Down for providing me with the files I needed, as I was away from my computer when I wrote this.