M$ will be supporting XP till at least 2014 that is at the very least another 5 years + of use of this product and maybe even longer if Windows 7 Doesn't live up to the promises that M$ has made for it.
If you remember back to before the release of Vista that was suppose to fix all of the problems associated with XP not only didn't it but because of the Problems that it introduced Business avoided it like the Plague so if 7 doesn't do all it is supposed to do Business has no need to even consider it as an Alternative to XP.
Currently Vista certainly isn't XP Successor and as 7 is a Tarted up Vista it may not be either. As 7 is yet to be released you need to allow at least 2 years of further XP deployment till business has made up it's mind about what their alternatives are. Remember XP was not adopted widely by business till well after it was released for sale so it is not logical to expect another M$ product to be so easily accepted. The Fact that Vista Bombed will not be much of a help to 7 either it has a long hard battle to win people and Business over. I personally think you'll find that Vista gets ignored just like ME did or maybe 2000 which was not as widely adopted as XP has become.
Col