Similar to the Mod Installer Generator, people can make scripts for mods and then the people who download the mod can have it automatically be installed, according to the commands in the script file. You also have the ability to choose which car to replace! You should definitely download this if you want to easily install custom vehicles and mods! It also includes script support and it works with mods. If it's not, then GMI can automatically install the mod no download required. It can also convert GTA3 cars to Vice City, and Vice City cars to GTA3, and it can also automatically detect whether or not the DMagic1 Wheel Mod is installed.
It also works with just about ANY custom vehicle downloaded from any website and you can even select the ZIP or RAR file you downloaded to install the car. This program works with both GTA3 and Vice City. It can also automatically search readme or text files that come with the custom car and find the handling.cfg, default.ide, and carcols.dat info for that car and automatically insert it into the game.
It has the ability to automatically search for the vehicle's DFF and TXD file and insert it into the correct IMG files. This program allows you to easily install custom vehicles and mods.