Last week Michael Riva wrote and article to ISASERVER.ORG about IAG 2007 that explains in details and in a didactic manner hwo to customize the IAG Portal. The article was edited by Tom Shinder and it is now available in the link below:

http://www.isaserver.org/tutorials/Customizing-IAG-2007-Portal-Pages.html

 

Really worth to read it if you are looking for this kind of documentation.