Hey!
I've actually taken the aforementioned train once as I didn't trust Asian domestic airlines then.
The trip is approximately 24 hours each way, and is a phenomenal opportunity to see the country side and mingle with the locals. The train is extremely safe and the crew is very professional, and I believe the train has no intermediate destinations although it does stop occasionally at stations to refuel/resupply.
If I recall correctly, there were three classes and every ticket includes a sleeping berth. Luggage storage was on a first-come, first-serve basis.
The only gripe I had was the restrooms in "economy", which were pretty much an exposed hole leading down to the train tracks.

If you walk forward a few cars to the private-room cars, however, there are actual metal toilets which made the trip much more bearable.
Check out this link for schedules and prices:
http://www.seat61.com/China.htm
Save a horse: ride a cowboy,
JC