A short summary is here: http://www.infoq.com/news/2009/09/Apple-Microsoft-Site-Usability
And the full article with web site screenshots is here: http://www.webdesignerdepot.com/2009/05/apple-vs-microsoft-a-website-usability-study/
The summary is very good for a quick look, it highlighted some key points make the two sites different.
Browsing Flow
Well designed flow of browsing leads user’s browsing actions. Keep pages simple but always provide "Learn More" link to drive user browsing and discovering.
Design of Navigation
Apple’s site try to give user a simple way to navigate and give user a consistent experience of easier navigation.
Readability
Large font size, enough white spaces, vivid color but not over use.
Consistency
Microsoft did a horrible work on keeping consistency, one of the reasons may be Microsoft has much more products, sites and teams which managing those sites and products in their own way. But is it a mission impossible for the giant creating and following a single visual design standard?