Here are a couple of sites that will teach you how to reverse engineer.
http://protools.cjb.net/
http://neworder.box.sk/codebox.links.php?&key=cracking
http://www.reverse-engeneering.de/
http://members.aol.com/jpeschel/progver.htm

Please do not use this info for software cracking and stuff. This is supposed to be used for learning, and not malicious purposes.
~thanks