How to create ray line from cloud in the sky?

[cnviewer]

There are always some beautiful photoes shown in the web , Im favourite at some scenery pic, espacially a bound of ray lines comes through clouldy sky. what is steps to create the effect with photoshop6.0?
2]
In rgb mode, we have 3 channels. if we set up the 4th channel for effective, what color does it act as?
(gray, or light channel?)

thanks

cnndt@yahoo.com