Hell, I'll tell you. But you ARE going to screw it up, and it WILL only work for one map, and you will PROBABLY replace a model in that map. Did I mention that you will probably screw it up beyond fixing, and your map will probably be corrupted and unusable? Good
1. Get WinMPQ
2. Make your map
3. Rename the skin and everything of your model to something that you're not using in the map. Change the model's skin path so it uses the old skin
4. Open your map and import the model to the proper path
You're not gonna get me to tell you any more than that, its horrendlesly outdated