The Fukin Prophecy
RIP Champ
All you need is OpenIV, an ASI loader and the ability to pass a 4th grade reading test to mod IV...I didn't think GTA IV had anything. Could be wrong though, but I thought it was all done outside of Rockstar tools.
Edit: Yeah, It's not moddable right out of the box. There's no official support
http://www.gtagaming.com/downloads/installation-help
And you gotta be at the "right" version. It's all a mess
Update 1.0.4.0 is preferred because it is the most stable but all versions of the game are just as moddable...
I mostly play EFLC...