how to select all checkbox?

I have n checkboxes and 1 checkbox 'SELECT ALL'.
for example:
<form action="" method="get">
<input name="sa" type="checkbox" value="v"> select all
<input name="c1" type="checkbox" value="v"> option 1
<input name="c2" type="checkbox" value="v"> option 2
<input name="c3" type="checkbox" value="v"> option 3
...
<input name="cn" type="checkbox" value="v"> option n
</form>

I'd like check all checkboxes when I select 'sa' (select all) and deselect
all boxes when I select one checkbox (less the checkbox I had selected)
How can I do that?
Thank you in advance,
Andrea.
Received on Tue Oct 18 03:03:54 2005