Hello, 
Installation : 1.ADD the ddf's and cols files in gta3.img
2.Copy tr.IDE and tr1.IPL to  data/maps
3.Replace the gta.dat files OR Add ( IDE DATA\MAPS\tr.IDE Under IDE Lines And IPL DATA\MAPS\tr1.IPL Under IPL Lines ) In gta.dat file
More is Coming :
this mod is made by Skann, for more informations contact me : Skann@live.fr . 