Transparent windows

Hi, I have been looking around the net for the secret to those black, transparent windows Netflix and others put up when there is a nested window. Its got to be something besides the css transparency filter because it works in Firefox.

Any tips or urls are appreciated.



BTW found this related to PNGs and IE
http://homepage.ntlworld.com/bobosola/pnghowto.htm

[SOLVED]
Here is a simple Javascript run photo gallery I just made (use it if you like)
http://www.geocities.com/spilledink/gallery.html

*No-AJAX script.