The glory days of these two windows version(windows Xp and windows vista)is long gone.
Apple is intending to release new security updates which will see windows Xp and windows vista un-supportable. Meaning, the new security update will make it impossible for Operatng systems like windows vista, windows Xp and Apple TV first generation units to use iTunes Store.
Apple made it official with a statement below.
If you have windows Xp or windows vista, your computer is no longer supported by Microsoft and you are not able to use the latest version of iTunes.
Although the previous versions of iTunes will work on these platforms but it's users won't be able to make new purchases or download recently purchased items.
If you are amongst those that would be affected by this new development, it highly adviceable to upgrade your computer to a higher version of windows, windows 7 probably.