A light source almost always has a diameter, resulting in a soft edge of the shadow.

If you understand german, http://www.amazon.de/exec/obidos/ASIN/3898422240/qid=1053790830/sr=2-1/ref=sr_aps_prod_1_1/302-5544559-6900002 is a good start, i don't know if there is something similar in...

Its a very good book to go further.
But its a book dedicated to mental ray, host (says: Maya) specific iusses are not covered. Additionally you should have a rather solid background in rendering, as...

Some of the common HDRI lightprobes give good results if used as a background image.