Authorization to proceed checkbox

My client wants me to implement a pop-up check-box that reads “I have read and understand yadda yadda yadda”…then they check a box, and possibly enter an email address to be stored in the database.

The process would be:
-visit home page
-click on link to a sub-page in the nav menu
-either before or after the user is directed to the sub page, the popup box would appear.

Anyone know of any extensions for this? or, any suggestions?

Thanks!