You'd jhave to import, texure, etc. The difference between BSP in games like UT2k4 and Halo is the BSP was an alias, it wasn't exactly a BSP mesh, they just work differently. So no, there is no "BSP Editor" For Halo, you'd hafta find a model decompiler/importer/import MAXScript, and then import and export as a .jms when you've textured it.