Terms and conditions plugin

Hi – hope I am posting this in the right section.

I am looking for a plugin that will allow me to put together terms and conditions which should popup on a separate window when a user first visits the site. The user should not be able to access the site unless he/she selects agree. This has to apply for any visitor (not specifically logged in users with account) to my site.

I have searched around for plugins like this, but could not find one that performs the above.

Does anyone know of a plugin that might help?