models actually use the format .mdl0 in Brawl.
To get a model from another game into brawl, it needs to be imported. Many Wii games have mdl0 files that can be imported; however, games with .dae models have recently been figured out.
http://forums.kc-mm.com/index.php?topic=17547.0What you're asking for is impossible at the moment, since.mdl0 files are only used by wii games.
Perhaps in the future, other formats will be able to be imported, but for now, anyone wanting to make a Halo hack has to do it custom style.
I honestly don't know too much about all this stuff, but this post is a gathering of all my knowledge from poking around the forums. If anyone has additional information, please post.