QUOTE
XP will be outdated before you know it.
It's been outdated for years in the features department (Linux and OSX overtook it long ago) but it can mostly be augmented with whatever you need. Vista just added way too much and made it too bloated. If XP is fine now then there's no need to worry for another 3-4 years. People still happily use 98 and ME at the moment despite their age. Considering the amount of people jumping ship to alternative operating systems (i.e. Ubuntu Linux is now estimated at 30 million users and now Dell are taking it seriously by selling it alongside Windows). Microsoft is really fading away, just very slowly. Internet Explorer has decreased in popularity, OpenOffice has matured and other projects, both open and closed source are competing. Linux has MASSIVELY evolved over the past two years and OSX (despite my massive dislike for Apple) has made headway into the computing world again because of the iPod. Given a couple more years, it's perfectly possibly for the Windows share in the desktop market to drop to a good 75-80%. By then, major companies will really invest in Linux or OSX (depending on which has the larger market share) and there will be little point using Windows any more because the competition is far superior and will have the same support.
Microsoft have their fingers in too many pies and, while they can make a good office suite and a few other decent things (Media Player isn't too bad) they're being beaten back on most fronts and will slowly fade away. Remember that Apple was on top in the desktop OS market once, they were only beaten when IBM came along in leaps and bounds in the desktop market.