okay that's pretty easy to tell you. and good timign as road warrior mad max is likely to start releasing our finished vice city models.
tools needed:
.img tool <-----this will get the models in game directory as well as the textrue files
notepad <------- hadelign and carols may need to be fixed notpad does it fine.
first things first...always back up whatever files your replace thats very easy process. and i should break down the files names to give you an idea what your usualy looking at.
file names:
.dff <------- actualy car model phrased for theg ame engine
.txd<------ the file that is the skin of the object in the game engine
now backing up files:
1.open the .img tool and look for a file in the gta directory called "gta3.img" (yes file name was not differnet form gta3.)
2. find the .dff file name of the vehicle you are replacing (ie: if the car in the mod files says comet.dff then look for "comet.dff" in the img directory.
3. once the .dff is located right click and click on "extract" put the orignal .dff into some folder you know you will look in if anythign shoudl go worng.
4. find the .txd file same name jsut look for "comet.txd" extract
done if anythign goes wrong jsut use the .img tool to reinsert the .dff and .txd of the original game model.
next adding the modded .dff and .txd file
1.open the .img tool if not already open.
2. find the .dff file of the car you are replacing
3.right click "delet" (saves you alot of heachaches later if you delete it jsut be sure you backed it up first.
4. find the .txd file of that same car in the img directory delte it as well.
5. click "add" find the modded .dff file whereever you extracted the downlaoded car from and click on the .dff do the smae thing with the .txd file.
6. click "rebuild archive" aslo save you alot of glitches.
done installign the car but that's only half the fun
1.close the .img tool once archive is rebuilt.
2. got to the actualy data folder in yout gta directory and look up the a file called "hadeling." reight click and make it "open with" say notepad
3. readme file for the modded car your downlaoed should have a handeling line. open that readme and copy that line....now in notepad look thought the handeling listing for the car you jsut replaced highlight the text in the hendeling file and right click "paste" the line should now replace theo ld hadelign line.
4. sometimes carols will need to be edited as well carols are the files that tell the game eninge what color to render the .txd files.
look in the same data folder for a file called "carols" open that with note pad if the read me has a carol line then repeat the steps listed for hadeling.
if done right vice city shoudl boot up fine and when you get to where the car you replaced spawns you should see your brand new mad max or road warrior vehicle in all it's glory.
if your confussed and i'm sure you are go here and look up "installig ncars in vice city"
http://www.gtaforums.com/?showforum=109
hope that helps good luck.