I receive a lot of questions about how to setup a Highly Available (HA) EDI Accelerator 2004. Here’s a link to a document that describes how to set that up: Configuring the Covast EDI Accelerator for BizTalk Server 2004 for High Availability (1063k pdf file).
Note: This is for the 2004 version only!! The 2006 version (see previous entry in my BizTalk Blog) has a more natural failover capability, that does not need extra configuration.