Agree before entering page javascript code is a useful utility tool to enforce any rules you may have and requiring the viewer to accept terms in order to access the page.
Live Example Below:
Simply Cut and Paste Script codes
You may add target="_blank" for page to load in a new browser
form action="http://www.your.com" method="GET" onsubmit="return checkCheckBox(this)" target="_blank"
Be sure to properly place scripts positions in head & body of html
This script has been in the DesignerWiz.com Public Library.