i have written a short tutorial on how to install wildfire on a mac on my blog: http://wibi.homeip.net/wp_en/index.php/archives/2006/04/21/tutorial/
hope this helps.
cheers
joerg
PS: check out this thread (http://www.jivesoftware.org/community/click.jspa?searchID=-1&messageID=100771) for details on how to get java 1.5 running