a Question about Transparent Background

I am doing the work of gui development.Occasionally,i notised that in windows system,i can create a window with entirely transparent background if only i set the HBRUSH type property hbrBackground of WNDCLASS struct to 0(which means "HOLLOW_BRUSH").
But unluckly i haven't found this function for windows in X Window System.I think that transparent should be a basic color meaning no any color,just as in many cases zero means nothing,while in rgb 0 means black.Black means no brightness,transparent means no changing,they are two basic null.Somebody tells me you can copy the desktop background image to your window rectangle,but this is only the simulation of transparent,and not equal to what i mean.
I know in X Window System one can create a image with transparent background,but may not create a transparent background window as i mean. Can you give me some advices?
______________________________________

×¢²áÐÂÀË30Õ×Ãâ·ÑÓÊÏ䣨 http://mail.sina.com.cn/chooseMode.html £©

===================================================================
°ÁÈËÉí×Ë£¬ÐÔ¸ÐÒ»ÏÄ (http://ad4.sina.com.cn/shc/zhuiyu_hprefresh1.html)