Instructions
Installing Building Mods
Go to a "GTA: Vice City" mods site and download the mod you want.
Extract the files from the archive, if necessary, and launch the mod installer.
Follow the on-screen instructions to complete the installation.
Installing Individual Buildings
Download and install GTA IMG Tool 2.0.
Go to a "GTA Vice City" mods site and download the buildings you want to insert in your game.
Open the folder containing the downloaded buildings and identify the .txd and, optionally, the .dff files. Write down the names of the files, as these are the files that will replace the files of the original buildings in the game.
Run the GTA IMG Tool. Click "Open," navigate to your "GTA Vice City" installation folder, select the file "GTA3.IMG" and click "Open."
Go to "Edit," click "Find," type the name of the downloaded building files and press "Enter."
Select the found results. Click "Command," then "Replace." Browse for the files you downloaded and click "Open."
Confirm when prompted to overwrite the files. Go to the "File" menu, click "Save" and close the GTA IMG Tool.