Open SparkIV and playerped.rpf that is located Grand Theft Auto IV > PC > Models > Cdimages.
Here are all Nikos clothing. The ones you are replacing are:
uppr_diff_014_b_uni.wtd - Upper part
lowr_diff_007_a_uni.wtd - Lower part
Find the files in SparkIV and export them, before you import the replacing ones.

There we go, now we only miss the optional gloves, balaclava and bag!
hand_001_r.wdr - Gloves model
hand_diff_001_a_whi.wtd Gloves texture
sus2_001_u.wdr - Balaclava model
sus2_diff_001_a_uni.wtd - Balaclava texture
suse_001_u.wdr - Bag model
suse_diff_001_a_uni.wtd - Bag texture
Find these in playerped.rpf and export them, after that replace 001 with and 000 and threw them in back there. Remember to make backups of the existing 000's first, or you will be stuck with having the balaclava, gloves & bag forever, as I am. lol.gif Remember to SAVE the archive in SparkIV before closing it down.
There we go! Everything's installed and everyone is happy, hope you like the skin!