GTA SA 3.0 (bought on Steam) does not allow mods in gta3.img.
Now with this plugin asi, you will not have problems in installing mods in gta3.img.
This mod requiere a ASI Loader to work.
If you need of a ASI Loader, use the Silent's ASI Loader: http://www.gtagarage.com/mods/show.php?id=21709
More info in readme.txt
Source included on download.
Mod by Fabio
Thanks to LINK/2012