I think Hyperterminal must be lacking the proper functionality for high speed communications, but I don't know why. There are many many other DNC utilities out there that will do the job properly. I started out using a simple program called Shadcomm (from the Millwrite engraving people), but now that I have OneCNC, I use their utility.
I think OneCNC had a free to try DNC utility somewhere, with a nag screen , but I cannot find the link to it at the moment. You could contact the Florida office maybe they'll have a link for you.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)