IMG Tool 2.0
This tool support GTA 3, GTA Vice City and GTA San Andreas.
Created by Spooky.
Unfortunately, for GTA San Andreas this tool only able to add file one by one. Not recommended for mapping mod, but can be used for add/ replace ped or cars or other mod that only have a few files.
This tool seem have problems with Windows 7.
Tutorial (for example) from these videos below :
