Ppl asks how to modify/import textures, so I decided to translate my italian tutorials for you.
Credits to me and my site GTA-Expert.it, do NOT copy this without my permission
Excuse me for my bad english, my english-to-italian is excellent, but my italian-to-english isn't so good, I'll translate my italian tutorials for you

Hope screens could speak more than 1000 words
I'll correct al my english errors with your help
Introduction about texturesYou could modify all .wtd textures in the game.
Don't confuse .
wtd with .wdr files:

WTD [Windows Texture Dictionary] are textures files.
WDR [Windows (gtaDrawable)] are 3D model files.
Example:
w_mp5.wtd:
MP5's Textures w_mp5.wdr:
MP5's 3D Modelyou could edit/modify textures with OpenIV or SparkIV.
I think OpenIV is
better, 'cause modifies textures levels to 1, so we have a better quality of the image in game. Anyway, ?ve made both tutorials for you.
Tutorial: Importing Textures with SparkIV Link
Importing Textures with OpenIV
Time: 10-15 minutes
Difficulty :
Software & DownloadsOpen .wtd files with OpenIVFirst of all, extract OpenIV archive files and open "
OpenIV.exe".
Image.
Clicking on "
File" > "
Open Content", OpenIV will automatic load GTA IV Main Folder, loading all relative files. You could view all gerachy files and view some previews.

In this tutorial I'll modify Niko shoes with my
Nike Air Max Plus.
We'll modify "
feet_diff_001_a_uni.wtd" located in playerped.rpf (
\Grand Theft Auto IV\pc\models\cdimages).
Find it like in the image:

Click on
playerped.rpf to open the archive and show files.
There is a list of .wtd files. We know that in our tutorials we'll edit "
feet_diff_001_a_uni.wtd".

BE SURE TO BACKUP YOUR FILES BEFORE EDITING ANY FILES!
You could backup "
feet_diff_001_a_uni.wtd" clicking on "
Edit" > "
Extract".
Edit a texturesSelect "
feet_diff_001_a_uni.wtd" and right click on "Edit".

You'll have the textures files list on the left, in this case only
feet_diff_001_a_uni.dss regular 7.

So, now you shoud have a .png file with your new texture.
Be sure that .png new file has
same resolution (in our case: 256x256).
Click on "Replace" and load
nike_squalo.png file.

IMPORTANT: Click on
Change Levels and edit value to
1.

Now click on "
Save" and press enter when DOS Window will open.

IMPORTANT: To apply modifies, click on "
File" > "
Rebuild".

Close the program and launch GTA IV.
Hope this topic is helpful!
This post has been edited by Fabio206 on Jun 2 2010, 00:40