The list of exams in Microsoft certification website includes the following test for BizTalk 2004:
Exam 74-135: Developing E-Business Solutions Using Microsoft BizTalk Server 2004
However as of 4/19 there is no link to the exam overview page, but if you replace the exam number in the url for any other test page, i.e. http://www.microsoft.com/learning/exams/74-135.asp it shows that this test has been available since Jan 17, 2005. It may be just a mistake on the site, anyway I've been looking forward for this exam to be released and I'm planning on taking it sometime soon.