Unpack the contents of the archive with the mod into the created folder. replace gta-vc.exe in the game folder or increase the limits up to 5000 in infonode, 8500 buildings, 4200 dynamic.
Option 2: Unpack the contents of the archive into the game folder. Further using IMG editor replace files from img to gta3.img or add to a new img using "IMG for mods "