Apple has stated
on a support page post that it will be dropping support for Windows Vista, XP, and the first generation of Apple TV on May 25th. Apple states that on Vista and XP machines, you will still be able to use older versions of iTunes without support, however you will not be able to make any purchases from the store.
Apple is more blunt about the 1st generation Apple TV, stating that "Security changes will prevent Apple TV (1st generation) from using the iTunes Store. This device is an obsolete Apple product and will not be updated to support these security changes."