For anyone that is downloading the BizTalk 2009 RTM from the MSDN downloads, you may have found that the Installation Guide.htm on the image refers to http://go.microsoft.com/fwlink/?LinkId=128383, which is the location of the BizTalk 2006 R2 guides. This link should be updated soon. As far as I know, no new installation guide has been released yet so your best guide is the 2009 Beta install guide download from https://connect.microsoft.com/site/sitehome.aspx?SiteID=218.
Once I hear about a new version of the install guide I will post more about this. Good luck to everyone trying out BizTalk 2009 RTM.