This sample shows how to call the BizTalk Business Rules from .net code. This sample passes in .net objects (using Helper .Net Components in the Orchestration) as facts and gets updated values returned from the rules engine. It also uses a long term fact creator defined on the Policy to cache long term facts. Make sure you read the ReadMe.txt for set up information.
This should work for both BizTalk 2004 and BizTalk 2006.
Get more information from the original blog post on this topic: http://www.biztalkgurus.com/biztalk_server/biztalk_blogs/b/biztalk/archive/2006/01/27/using-.net-components-and-long-term-facts-with-biztalk-rules.aspx