It is very true that boycotts only work if a sufficient number of people are involved; however, it is equally true that buying M$'s products does not help our cause.
I would also urge everybody to write to the appropriate parties to express your opinion; I even urge those who are fans of M$ to do so. Politicians are many things (well, mostly they're just corrupt), but they are definitely not mind readers. And given how easy it is to spoof e-mail messages, writing your thoughts down on paper is not a bad idea (heck, send an e-mail
and a letter).