Update: 7.0 is here but it is trialware.
There is an old FAQ from 1999 here.
The source code for Hyperterminal is in the Windows 2000 source code (htpe version 4) that was leaked.
If you are working with binary data or other difficult data streams, I strongly suggest using Realterm instead. To quote their page:
Realterm is a terminal program specially designed for capturing, controlling and debugging binary and other difficult data streams. It is far better for debugging comms than Hyperterminal. It has no support for dialing modems, BBS etc - that is what hyperterminal does.