How can i get the itunes update?

i have windows vista, i tried to buy a snl vidio for my ipod but it said i needed the itunes update, so i clicked on the upgrade on and it brought me to itunes online, i clicked the download now on and waited for 10 hours for it to load, when it was done, i clicked on shop now and tried to buy my vid but it still said i needed the upgrade? what did i do wrong and how can i get the vid? please help me!!