Hi Geoff;
Like John's, my Nisus-related files are:
~/Preferences/com.NisusWriter.LSSharedFileList.plist
~/Preferences/com.NisusWriter.LSSharedFileList.plist.lockfile
~/Preferences/com.nisus.NisusWriter.plist
~Preferences/com.nisus.NisusWriter.plist.lockfile
I'm running Lion, but I think this setup is standard throughout OS 10.
Hope this helps
Ray