Laurie,
You would normally only put a symlink in rc7.d not the actual script, most scripts would reside in init.d. as you can see from Ray's example of dansguardian.
Check that the start script for twonkyvision is init.d and then do as Ray has shown, replacing dansguardian with the name of the startup script for twonkyvision. The number 92 only determines the load order of links in rc.d the highest being the last to load.
Regards
Jack