1. Download a program called OpenIV and run it and find your GTA IV Directory. ( WHEN You run OpenIV, make sure you RUN as ADMINISTRATOR)
2. Car mods: On Open IV (look up top and you will see a little box called "edit mode" click that and say yes. Then find (Grand theft Auto IV-PC-Models-CDimages-Vehicles.IMG) once you see a view of a crap ton of vehicle names example "police2.wft/wtd" Car mods step2: (example) have a police car mod that has police.wft & police.wtd.) Put the 2 files to your desktop then drag and highlight the 2 files and drop them in the OpenIV Vehicles.img. (NOTE: If they don't transfer then you have to replace the models individually. by right clicking on the name.wft/wtd and go to replace)
3. Script mods ( ELS, LCPDFR..... ) go to google and type in "gta iv .net scripthook" download it from the website that shows up. open your Grand theft Auto IV directory folder. open the scripthook file and drag and drop all the files to your IV directory. then download the newest version of lcpdfr and do the same thing. there even should be a read me file to show you instructions.. then hey if u want ELS do the same thing Lol!
4. Weapon/ped models look up on google "how to install gta 4 weapon mods" "How to install Gta 4 Ped Mods" (its a bit different then installing car mods)
5. sound mods look up a tutorial on google.. although the directory for sounds is " Grand Theft Auto IV- PC- Audio- SFX"
(NOTE: IF YOU DON"T HAVE WINRAR, DOWNLOAD IT. Ya KINDA NEED IT :P)
Hope that help! :P - Tooth