I have added 3 widgets in the footer using this (to give the footer the appearance of being a continuation of the sidebars above (i.e. the widths are same as for the page)):

<?php bfa_widget_area('name=My widget area&cells=3&align=2&width_1=200&width_3=200&befor e_widget=<div id="%1$s" class="footer-widget %2$s">&after_widget=</div>'); ?>

What I would now like to do is add a dashed vertical line between widgets so it appears to continue the theme above. What should I do, please?

try this

td#my_widget_area_1 {border-right: dashed 1px #000;}
td#my_widget_area_3 {border-left: dashed 1px #000;}

Thanks - so where do I put this code?
(I'm still a learner in this!)

put it in ato->Add HTML/CSS Inserts->CSS Inserts

Many thanks - looking good (I seem to need to adjust the widths to 190px and adjust the line color, but I can do that I think).
This is my first web site and is great fun, thanks to Atahualpa for such a flexible theme!

This is what I ended up with:
td#my_widget_area_2 {border-right: dashed 1px #cccccc;}
td#my_widget_area_2 {border-left: dashed 1px #cccccc;}
td#my_widget_area_2 {padding: 5px}
The padding was to get the text clear of the border.