I can help you if you want. I'm a GTA IV Mod developer and software developer so i know how it works.
At first i need to know what kind of mods you want, if you want the "newest" mods (mod loader is from 2009) you need to
download .NET Scripthook from www.hazardx.com
, also you need to download from his website YAASIL (Yet Another ASI Loader) this file is called "dsound.dll". Be sure to update your GTA IV game to version 220.127.116.11 or when you have EFLC to update it too.
Copy the dsound.dll file and the scripthook files to your GTAIV Main directory. Go to the folder properties and allow everything under the security tab.
Start the game and press the key before the 1 key (left side of it) from your keyboard. This will open the console menu (if you hit the right key). Now you installed the mod loaders. To install the mods download .NET developed mods that scripthook can load. The extension of these mod files are most time .net.dll or .net or .vb or .cs
Also i've mods available, unfortunately for you the whole system has been changed (my mod system).
I'll upload soon mods that i've developed to my website.
Also i want to help you with programming mods for GTA IV if you want, but you need to check out my website for it, you can find website address in the contact below:
Personal email: email@example.com
Hear from you,