The W-9 isn't so you get charged tax, it's so that when Microsoft (or whoever) is filing with the IRS, they can claim you as being a legal resident and receiving some sort of payment/gift.
When you win a certain amount on a lottery ticket, before they cut you a check, they make you fill out a W-9 or a similar form, and you may have that included as 'income' when you file taxes. So no, this isn't probably going to be 'free-as-in-beer', but it'll be close. =)
By the way, it's snowing outside.