need help on shadow map !

Hi,
I am trying to code shadow map technique, I have read lots of paper and I have understood the technique.
But how can we implement that with opengl ?? and using extension ?? I have downloaded the example of nvidia but they use their own library and there are no explanation in the code !! no comments and no papers !!

Does anyone have a link to a simple source code with comments …

shadow maps are an old technique, it must exists somewhere !

thx …

ps:I am very hungry against nvidia sdk …