Ahh yes, the infamous skins...
They do work, although I haven't tried using them with 2.3.
I'll dig the files up and double-check later, but if memory serves, you need to overwrite the skin files in objects_statics_client.zip.
You can't extract files into an archive, you'll need to extract the new skins somewhere, then open objects_statics_client.zip, navigate to where the skin files are, then drag-and-drop the new skins into Win RAR (it'll overwrite the old ones). Don't forget to make a backup first.