There are lots of websites and youtube videos all trying to tell you how to mod GTA IV. Unfortunately, they’re almost all out of date, or youtube videos.
I’m using steam installed Grand Theft Auto IV 1.0.7
A decent guide: http://www.gta-modding.com/iv/tutorials
Prepping the Game
Install This:
Xliveless (v0.999b7 md5: F7FD7512F6AC8959CDDA6A2B2E014C68)
http://www.gtaforums.com/?showtopic=388658
SparkIV (v0.7.0b1)
The original tool, currently trying OpenIV below instead of this.
http://www.gtaforums.com/?showtopic=384933
 OpenIV (v1.5.0)
Seems to be much newer than SparkIV. Still testing it out. It actually installs (as opposed to SparkIV, which you just unzip and run) and is more difficult to set up that it needs to be. Some mods require OpenIV.
http://openiv.com/
Installing a simple mod
Most mods will tell you exactly what to do in their readme.txt. I’ll only give installation highlights.
No Intro Screen
Who has time to look at intro screens? This mod is easy to install and well worth it. Just copy loadingscreens_pc.dat to common/data. It’s plaintext so you can see what changes it makes.
http://www.gta4-mods.com/misc/no-intro-logos-f1814
Rockstar Social Club
I couldn’t find a way to disable it. I added these to my hosts file anyways:
127.0.0.1 rsgames.hs.llnwd.net 127.0.0.1 mls.rockstargames.com
At least the time saved taking off the intro screens make up for having to click through the Social Club screens.
Installing some intermediate mods
scripthook.dll (v0.5.1 md5: 7260B388AAC8329C3CF615084AA7DB83)
You may need to dig around for this download; the download link in the homepage is dead. Sometimes it’s redistributed inside a mod. Just copy it into root GTAIV directory.
homepage: http://www.gtaforums.com/index.php?showtopic=390582
inGame Trainer (v1.9.0)
This is the trainer you see most often in youtube videos. You can change the weather, teleport, change your wanted level, enable god mode, and enable cheats. It’s not an open sandbox game without a little god mode.
homepage: http://www.gtaforums.com/index.php?showtopic=393676
CarSpawner In-Game Menu
The thing about this mod is that for some reason, the readme is a word doc. Don’t worry though, the text on the homepage is the exact same as what the readme says. This mod defaults to taking over F1 to open the gui, just like inGameTrainer, so you’ll need to edit at least one of them.
http://www.gtaforums.com/index.php?showtopic=399468
Installing an advanced mod
Iron Man IV (v1.2)
See the readme.txt. It’s an involved process but detailed nicely. Remember to make backups!
homepage: http://www.gta4-mods.com/player/iron-man-iv-v11-f21888
Other noteworth mods:
- iCEnhancer
Other hacks
commandline.txt
http://www.gamefaqs.com/pc/952150-grand-theft-auto-iv/answers?qid=20326