Please keep spoiler discussion in this thread prior to the episode's airing. I will post a separate thread for post-episode discussion. I am also going to put each episode's description and guest casting in the spoiler thread in case some posters want to be completely spoiler-free.Hopefully, I won't screw up the font color again. 
Episode 6.04 "The Substitute" Locke goes in search of help to further his cause. --Locke-Centric-- Guest starring: L. Scott Caldwell as Rose, Katey Segal as Helen, Billy Ray Gallion as Randy, Suzanne Krull as Lynn Karnoff, Kenton Duty as teenage boy, Eddie L. Cavett as courier and Joshua Smith as school kid. Written by Elizabeth Sarnoff and Melinda Tsu Taylor. Directed by Tucker Gates.
LAST EDITED ON 02-16-10 AT 10:06 AM (EST)Thanks for the spoiler thread mrc.
Here is a link to 3 short promos for the episode....
http://www.lostseason6.com/
This looks to be a great episode with Locke in 2010, where he and Helen are going to be married soon, as per the promo. (We see Helen in the guest starring credits - Katey Segal) Also, it shows him getting fired. So, more differences post the "incident". It appears that Locke did go on the walkabout as he told Boone on the plane that he had...
Then, in the present on the island, we see a clip where XLocke and Sawyer reconnect, and then later they are seen with James going over the cliff with the rope ladder....off to read the "writing on the wall". Can't wait for this!
The last clip may be a promo for the entire season, but if it's just one for tonight then, WOW! What an episode this will be. We see James pull a gun on XLocke, XLocke vows to tell him/them? everything he knows. We see that Jin gets back to Ilana and gang and SUN, looking forward to that reunion! But, Richard is telling them that "he" wants everyone dead, everyone you know!....WOW! Can't wait.