Microsoft is far from dying, and you should know that. Yes, Apple is growing, but you are delusional if you think Microsoft is dying. I'll give you the point of uncertainty now that Gates is gone, but it's not like they're running around like chickens with their heads cut off.
Microsoft Income Before Taxes (in the last 3 months): $4.8 billion
Apple's Income Before Taxes (in the last 3 months): $1.5 billion
Microsoft is coasting along on their Windows and Office monopolies, raking in huge revenue figures as usual. In this way, they actually do resemble a chicken running around with its head cut off, because they've made years worth of poor executive decisions which are manifesting themselves in numerous ways: the disasterous Vista launch, their ineffectual attempts to compete on the Internet, their cash-hemorrhaging ventures in entertainment, the failure to establish PocketPC/Windows Mobile as a competitive platform, their failure to impose their DRM-laden will across the digital landscape, and so on.
Apple and Google are pounding Microsoft in some pivotal markets, and the rest of the industry has taken notice and doesn't fear Microsoft as much as they used to. Of course you can't ignore a company with as much power and financial resources as Microsoft, but smart companies can and have beaten them in the market time and time again. I think enough companies that partnered with Microsoft over the years have gotten tired of getting screwed over and are looking for alternative ways to go.
As long as Ballmer runs the show up there, Microsoft's malaise will continue.
And I don't see Apple taking over the #1 OS slot ever, ever, ever. Windows is so entrenched it will take a long, long time for it to lose its overwhelming grip. I think some distribution of Linux will make great enough strides to become a mainstream OS at some point (Ubuntu seems the frontrunner at the moment). Apple will keep growing, mostly on the higher end of the market and will continue to draw more previously Windows-only developers into the fold. Best case scenario is that Windows, Mac OS X, and Linux all end up strong enough in the marketplace to keep everything balanced and interoperable. However, even a market share split of 60% Windows, 20% Mac OS X, and 20% Linux would take many years to unfold.