Mikrotik Hotspot Redirect

Here’s what I’m trying to set up:

When a user connects to a Mikrotik hotspot, their browser is immediately redirected to a legal agreement web site. There, they must click on “I agree” to proceed.

Seems like simple enough of a concept, right? I’m having a bear of a time figuring out how to do this. Any thoughts?

You must pass all the variables required for the login to an external page. This wiki might help with part of it. If you want the agreement page separate from the login page, you will need to pass the variables from page to page with a form (the “I Agree” button should submit that form) until the login.php page.
http://wiki.mikrotik.com/wiki/HotSpot_external_login_page

ADD: I don’t think that is a real good idea tho. I would put the agreement on the login page, or a link to the agreement on the login page. Otherwise, every time you login, or the login is rejected (invalid user or password, etc), the hotspot would display the user agreement again.