I am trying to achieve an email signup and verifier to access a page. 

As in, the reader sees the page, it darkens and a popup comes up that asks for the reader's email to continue. Once entered and verified it is real, the page is accessible from there on out.

Like so:

http://www.health.harvard.edu/newsletters/Harvard_Health_Letter.htm

Can anyone point me in the right direction? I know xhtml, css and some php -- pretty raw on js

Thanks.