This lab walks through two different types of message debatching in Biztalk. It shows how envelopes can be used with the Xml Disassembler to break up larger Xml messages into single messages. It also covers xpath in a loop inside an Orchestration.
Get more information from the original blog post on this topic: http://www.biztalkgurus.com/blogs/biztalk/archive/2005/07/12/XPath-Debatching-and-Envelope-Debatching-Biztalk-Lab.aspx