Debatching into single messages is easy with BizTalk 2004. This sample shows how messages can be groups into batches of any size inside an Orchestration using an external .net component. The external .net component uses streams to read the message from an Orchestration. The message is passed into the component as an XLang message type.
This sample should work in BizTalk 2004 and BizTalk 2006.
Get more information from the original blog post on this topic: http://www.biztalkgurus.com/blogs/biztalk/archive/2005/03/22/Debatching-Messages-Into-Smaller-Batches-In-An-Orchestration.aspx