Well, just try to make it clear to your boss that a quality platform for serving the big company's website is an investment, not an expense. Try to find some statistical information on how much faulty Microsoft software has cost major companies in headaches and lost revenues.
I can tell you with near certainty that if your website is huge and heavily relied upon for the well-being of your company, It will cost far more in Man-Hours and Lost Time to deal with problems caused by yet-another-crappy-product-from-MonopolySoft than it would cost to pay for hosting on a unix box.
just an opinion...i'm sure many people are paid well to say good things about microsoft, and that many other people are ignorant enough not to know the difference. (Why is there a CD in my computer's automatic Cupholder???)
-dolphinsnot