Arcane University:Niftools/Chunkmerge for Skyrim
The Beyond Skyrim Wiki — Hosted by UESP
Nifskope/Niftools is a very important tool as it allows adjusting and modifying meshes outside of full 3d programmes in nearly the same rendering as in game.
Chunkmerge is a community standard to add collision meshes to a nif but it does have its limitations for specific mesh types.
grab it while its hot!