[Mark.B]

In template SHOWTHREAD find this:

<label for="qr_quickreply"><input type="checkbox" name="quickreply" value="1" id="qr_quickreply" accesskey="w" tabindex="4" />$vbphrase[quote_message_in_reply]</label>

Replace with this:

<label for="qr_quickreply"><input type="checkbox" name="quickreply" value="1" id="qr_quickreply" accesskey="w" tabindex="4" checked="checked" />$vbphrase[quote_message_in_reply]</label>

This will tick the box by default, *however* I have always found if that if you then submit a quick reply using AJAX, the box unticks again which can be annoying, and I have never found out where the code for that is. I am guessing it must be within the AJAX code somewhere.