Just tossin' this out as possibilty, not sure how/if it would work.
In the add.cgi, add some code that would be like:
if ($agree eq "")
&site_html_add_failure ("You must agree to terms of service.")
And the checkbox would be be named 'agree'
This is just a starting point... I would rather do stuff with perl than java. If you need more help, I'll put my thinkin' cap on an see what smokes!
Leonard
aka PerlFlunkie