A good document details the three options you have for workflow with BizTalk Server 2004:
https://files.cnblogs.com/stevengeng/ChoosingTheRightWorkflowImplementationWithBizTalkServer2004.rar
Solution I: Orchestration with user interfaces such as InfoPath and portals such as SharePoint.
Solution II:BTS HWS with user interfaces such as InfoPath.
Solution III: Workflow ISV Partner Offerings(based on BizTalk HWS).
另外一个solution: BTS HWS+Microsoft MCS
