As part of my ongoing work with BizTalk, I frequently need to download versions of line of business or host system software to test integration with various BizTalk adapters. Determining the best place to get the software to setup VPCs for testing this integration takes a long time to find. I was working recently on setting up environments for Oracle and some ERP systems to work with the BizTalk Line-of-Business (LOB) Adapter pack. I found this link to the Oracle eDelivery site which includes many downloads to setup these VPC environments. Here is the link: http://edelivery.oracle.com/. This site includes available downloads for most Oracle products including ERP systems for companies recently acquired by Oracle like Siebel, JD Edwards, Peoplesoft and others.
Also, for really helpful information on integration in IBM environments, go to the search at http://www.redbooks.ibm.com/.