I can see Apple having a bigger market cap than Microsoft and being a bigger company in the next few years. They already have a better cash position and zero debt.
Increasingly people are using mobile devices for their computing needs. Apple is quite well positioned in this area going forwards, whereas Microsoft still needs to work out how each of thier various parts of the puzzle should come together (Win Mobile, Zune, the Danger team etc.). When this is worked out, I wouldn't rule them out, although the clock is ticking. By then RIM and Apple could have it all pretty much sewn up.
In terms of Desktop market share, no, that market is gone. Apple will keep plugging away and as long as they keep the profitable stake they will be happy. I think they do need to put more time into Mac OS X though to ensure this is the case. I feel from 2001-2004 Apple were driving development far harder than 2004-present.
In terms of server, well Microsoft has some good products here, but it this area is more competitive than the Desktop. Apple, however, is not one of the players.