Question on replacing old Model/Skins?

I had a new model & skin sent to me that I wanted to use instead of the julii hastati, but I'm having problems getting it to work properly and haven't yet received a reply from the sender. I can see the model working properly, the problem is that the skin won't work. Can someone please tell, if I have the following files, .psd, .dds, and .cas, where I'm supposed to put them to make the model work properly?
Thanks :help:

There is a tutorial how to add new units to the game in the Scriptorium, that should contain all the info you need (more, actully, since you just want to replace a model and not create a whole new unit).