I've just started working on a BAM project, so I started reading tutorials. Everyone was mentioning Excel add-in. I thought that it was an installation that you download from Microsoft's website, but after spending couple of hours searching for this add-in I realized it's just a plain Excel file BAM.xls located in \Program Files\Microsoft BizTalk Server 2004\Tracking (depends in which folder you installed BizTalk) that you need to copy somewhere else, because it's read-only. I felt so stupid! I hope I spared you some time looking for it.
Update: In BizTalk 2006 BAM Excel is no longer implemented as a Excel template, now it's a permanent add-in. If it's not available when you open Excel, click Tools -> Add-ins -> Business Activity Monitoring