This would be like a policy agreement on login.
ie;
User logs in as normal with user/pass, but before they are redirected to the forumhome page, theyare shown, and must agree to the forum rules - 'continue login' button would be disabled until they checked the 'I agree' checkbox.
(this would be in addition to the agreement during registration - and purely for forum access).
[Edit]
Basically, showing a modified version of the register_rules template
I hope that was clear enough..
Thanks in advance to all who reply.
Nobody has anything, or know of anything?
I know it would at least take a modified copy of the register_rules template and a few phrases, and possibly a few changes in the login.php (the redirect location).