How to display a custom block as a pop on home page?
There are other modules which provide you the popup functionality.


Popup message



  Display popup message for users once per browser session. Based on
  javascript code:
  http://yensdesign.com/2008/09/how-to-create-a-stunning-and-smooth-popup-...



Lightbox2



  The Lightbox2 module is a simple, unobtrusive script used to overlay
  images on the current page. It's a snap to setup and works on most
  modern browsers.



Shadowbox



  Shadowbox is a JavaScript modal media viewer application for viewing
  images, video, Flash and other content in a modal window.