How to skin a Campaign Screen?

I need the Night elf, thats on the background of sunken ruins, [in the Night Elf expansion] to be skinned.

How do i do that? where must i import it to make it show up?

Firstly, you have to extract the model. Then you skin it, do whatever you want with it. Next you have to implant it back into the mpq itself for changes like that to be made. Be warned, if you didn't back up the mpq, you might have to do some re-installation.

Unless he is making a custom campaign, then there would be no need to back it up.