I posted a letter on this subject a couple of days ago. There were a couple of folk who asked some questions and I tried to reply via the original letter, but I just don't know how to do this. No wonder that I do struggle with flight simulations from time to time !!
The address where the "FMC - VNAV Tutorial" can be found is:
This is a fairly recent addition to the site, +/- March 02.
I hope this helps! It certainly helped me !! I just wished somebody could compose a similar document for the FMC in the PSS 747. I still cannot get to grips with it !!