Now that I think about it some more, I doubt that MS can do what it has done in the past again. The OSS community seems to be much strong, thanks in no small part to companies like Google, who use it as a tool against Microsoft. MS is primarily a software company (although you can see signs of them trying to change this) competing against a new age of service companies like Google, Yahoo, IBM, etc. At the moment, it's in the best interests of the service companies to contribute code and money to the OSS community. It increases the values of their services which rely on OSS, and at the same time, cuts into markets where MS has dominated.
The fear that MS will somehow contaminate or kill linux, or OSS, is really misplaced. I think you'd see a huge reaction (particularly these days) before that could happen.