here are some files on the gta3 cd/dvd that can be simply edited with notepad.
the version i have of gta3 is 1.4 it is a pirated copy from indonesia, the US version. i can open it on my pc so it must have been put on a cd so some stuff might be missing. what i have noticed is that in allot 
of these files they tell you how to edit them, well they seem more like a message to the developers when making the game, it is very simmilar to what was in gta1.

i have named all the files txt so 100megsfee lets me put it online.


carcols.dat		 you can edit what colour the cars have(out of a range off availiable colors) so you can make emergency, taxi and gang cars different colours etc.
default.ide		 you can edit car and ped properties like what family a type of car would belong too, ie different driver. and you can make a car a plane by adding an antribute i think...
fistfite.dat		 you can edit properties about the different fighting moves, ie what animation to show, how long it takes etc.
gta3.dat 		 just a simple loading procedure file.
gta3.zon 		 you can edit zone properties, its abit confusing though, allot of the properties are to do with some of the other dat files.
handling.cfg 		 you can edit handling properties for cars, ie speed, turning etc.
map.zon 		 more zone stuff.
object.dat		 you can edit object properties, like elasticity and stuff. you can edit thing like trees, poles, windows(breakable glass)
particle.cfg		 you can edit the properties of particle stuff, ie fire.
ped.dat			 you can edit ped properties, THIS IS INTERESTING! you can make cops not get angry if they see dead bodys and who people are afraid of and stuff.
pedgrp.dat		 you can edit what people hang around in what areas, and time.
pedstats.dat		 you can edit pedestrain properties, how scared they get, how strong they are how much they break the law, etc. you can make yourself stronger and cops weak. you can even make cops break the law.
surface.dat		 you can edit surface properties, ie ground, road etc.
timecyc.dat		 you can edit the time/weather cycles.
train.dat & train2.dat   you can edit train properties, very complicated, couldnt be bothered working out, maybe later.
water.dat		 you can edit water properties.
weapons.dat		 you can edit weapon properties. VERY INTERESTING! you can do all kinds of stuff with this, you might even be able to add more weapons if you made new animations etc. i'll be looking into this one.

system.cfg		 you can change what file to load, version, and video mode, i'm going to see if my PAL ps2 can play gta3 if i change the NTSC to PAL and reburn it, prolly wont work. i need a chip... oh please god give me a chip.