Again, I know this is old but I will be happy to help. I've had a lot of practice adding artwork. Here's a tutorial I posted on RunUO a few years ago:
http://www.runuo.com/community/threads/ ... -to.54706/
I also have items to be added into the MUL files, both wearable (hair, clothing, armor, etc.) and non-wearable (decorations).