Cortana.org has posted the Halo Editing Kit tutorial today. Additionally, HBO has mirrored the directory in the event of server troubles; either mirror should work for interested modders. Some new screenshots of Sapien and Guerilla (the Halo resource editors) await; go and check it out!
Edit:Clarification, Bungie also gave the HEK tutorial to HBO - it was not mirrored in the event of server troubles.
Halo PC Editing Kit Tutorials
