How could I make an advertisement screen like this??

[maverick]

Hey,

I was just browsing around blogspot and found this website that has a front page ad screen that disables you to continue to the website without having completed the instructions of the front page ad/notification (I need to make something like this to get my website members to register before continuing to the website though still keeping the background visible), the ad is provided by CPALOCK.com but I read in the source code they use javascript for it, so how could I get a main page screen like this? :

http://getgooglewavefree.blogspot.com/

I know theres this box script: http://www.dynamicdrive.com/dynamici...ndow/index.htm but how could I make the rest of the page unclickable?