Please note that Microsoft's website is not hosted at Microsoft directly, but through NSATC.net and Akamai.com. Notice that when you ping google.com, it resolves to pinging
www.google.akadns.net. Akamai is used by multiple Fortune 500 companies to handle their network, e-commerce and web/dns.
I would suggest against putting Microsoft IP address to match the domain as it may change at any time. DNS machines receive updates all the time so that they are consistent, and if your hosts file is telling it to go somewhere else than where it should, you will have issues.
Try pinging lycos.com, yahoo.com, altavista.com (which yahoo2 comes up), etc....