So i was looking through the Sims 3 folder (/User/Applications/[Sims 3 GUID]/) and found the 'res' folder which contains, surprise, all the skins and clothes for your Sims. And their just normal PNG files. Looks like we could have a lucrative skin/clothing mod opportunity. I'm going to mess around and see if you can ADD clothes or only REPLACE them. I;m not very good on the art though so don't expect too much in the way of custom clothing packs coming from me.