Hi,
I am a new CC, I used to create for IMVU but I hid all of my products about 5 years ago.
One of the things that is a bit hard on me, is finding meshes to texture, on IMVU all you had to do was look for "Derivable clothing" in their product catalog, the meshes would be instantly accesable and you were ready to go, but for the SIms I have no idea how to retexture non-maxis meshes...
I want to state I do not intend to retexture or recolor meshes without permission. :)

Lzzles

When you use CASTools you'd select the "Clone Package Editor" tab and then hit the "Select" button right at the top (where it says "Select Package") to open the package you want.

Or do you mean the actual texturing is giving you problems?

For where to *download* meshes that you can retexture, there is no grand unified system .. on this site you'd just read the download post, and if that doesn't say anything, check the creator's profile to see whether they have a general policy on how you can re-use their stuff (that's either in the Policy tab or right in the main profile text). If you can't find any info you can always PM them and ask. I think most people who have their own sites also have a TOU page that should have the info you need.