The following work is based on the original thread:
Microsoft FY End Jun 2007 and FY end Jun 2008 – A MORE THOROUGH ANALYSIS
http://www.vgchartz.com/forum/thread.php?id=35336&start=0
Please read it carefully to see how the numbers were derived.
Before starting, these are some of the main assumptions that I made that can be questioned, and possibly changed.