I have a setup CD for XP SP2 - I have made TWO backup copies to ensure that I can continue to use it for the foreseeable future.
MS extended the extended support period for Win 2000 by 3 years (2007-2010) due to the demand / pressure to do so. I would not be AT ALL surprised if even mainstream support for XP were to be continued beyond 2010.
Vista? No thanks.