Mike,
Using the mouse and the graphic keyboard will not cause Hauptwerk to sound.
You can download a trial version of NoteWorthy Composer and with MIDIyoke (a freebie) you can try out the sounds to your heart's content.
When I am working in NoteWorthy I have the settings so that I can immediately hear my work using Hauptwerk.
Here's the url for NWC: http://www.noteworthysoftware.com/composer/
And here's MIDIyoke:http://www.midiox.com/index.htm?http://www.midiox.com/myoke.htm
(I'm not sure about the MIDIyoke site--it wouldn't come up just now.)
Here's another download site: http://www.hitsquad.com/smm/programs/MIDIYoke_NT-XP/
Hope this helps.