1. Download Spark IV 6.2.2. (This one works with patch 1.0.4.0)
http://filesmelt.com/Filehosting2/downloader.php?file=SparkIV0.6.2.2.zip

2. Run Spark IV. Go to "Open" Find playerped.rpf in "C:\Program Files\Rockstar Games\Grand Theft Auto IV\pc\models\cdimages"

3. Replace "uppr_002_u.wdr", "uppr_diff_002_a_uni.wtd", "uppr_diff_002_b_uni.wtd" and "uppr_diff_002_c_uni.wtd" with their respective replacements in this install folder.

4. Run GTA IV and they should hopefully work. The skins these replace are in the download picture.