Don,
Have you tried HS 2.1 yet? Copy your HS 1.7 install to a spare PC and install .Net and HS2.1 over the top. Run it. See what works / doesn't work. Upgrade all of your plugins to the latest for a fresh start. Report what works / doesn't work. I think you will be suprised on how much just works.
Run it in parallel. Put Watchdog on it to reboot if it takes much cpu / ram or is unresponsive. Have one PC monitor the other. Put one on one web port, the other on another so you can always remote in.
This is a pretty conservative way to validate that it will work for you.
Then, you will be up and running on the latest, supported product where all of the next HST and user development will be for.