Microsoft hasn't taken anything from Sony. Sony has lost a lot of market share, but it's been picked up by Nintendo, not Microsoft. Even in this supposed "HD Console War," Microsoft is not going to score a decisive victory.
That being said, barring a series of serious errors on the part of Nintendo, Microsoft will not be able to compete with them. Microsoft is not a very creative or innovative company at all, so the idea that they could come up with something that would have the kind of impact that Nintendo's offerings(Wii, DS, etc) have had on the market is absolutely nil.
The only way I ever see MS being market leader is if both Sony and Nintendo make some huge gaffes. Even then, MS probably wouldn't even have a majority market share, just a plurality as they wouldn't bring anything new to the market to capitalize on the situation.
Consoles owned: Saturn, Dreamcast, PS1, PS2, PSP, DS, PS3
