yes, I have used the HST Napco plugin with a 9600 system (which I have a bunch of parts for sale if you are interested...). It has been a while since I did the initial configuration but here is a high level:
Install panel and plug all hardware parts in (this takes tons of time)
Replace the controller chip with an optional HA chip.
Configure the panel either with their DOS or Windows program (neither are good examples of good software)
Plug a serial cable into the Homeseer com port and run it to the optional Napco HA kit adapter that came with the chip.
Install Homeseer on that PC. Upgrade to lastest build of Homeseer. Run Updater and see the Napco Plugin. Download and install it. You will need to tell Homeseer what your access codes are to get rights for Homeseer to connect with the Napco panel.
When you connect for the first time, Homeseer devices are configured with all devices configured in your Napco panel (that you configured with the Napco software).
Now you should be able to see Homeseer devices turn On or Off based on close / open state of the Napco switches.
You can then use state changes in Homeseer to trigger events etc.
Thats the high level.
