I'll have a try :-)

1st place to look:
http://talk.maemo.org/showpost.php?p=784834&postcount=1
This is a simple way of using the existing Phone Control scripts (http://wiki.maemo.org/Phone_control for reference)
The one called profileset can toggle between General and Silent - this was easier for me than the dbus commands in the wiki...

Create or otherwise get a General and a Silent .png file

Create a new QBW
In Beecon Statuses area, set the =0 to be your Silent .png file
set the =1 to be the General .png
In the Edit Command, if you copy the if statement in my other post and paste it here it should work straight off.

In Update Policies, set it to run on startup and on click

There will be other settings to change - I see lots of Hide "Yes" and Position "Hidden" - but the above should get you most of the way.

PS - standard disclaimer that I am a computer numpty and self taught through copying other people's good work