The TV shows are currently available to download for customers in the continental US, and will play on XP and Vista PCs and the Tivo set-top box.
NBC announced last week that it was not renewing its deal with Apple to distribute its shows via the iTunes store.
Apple claimed that the deal fell through because NBC wanted to push per-show prices as high as $5, while NBC claimed that Apple had refused to allow multiple episodes to be bundled at a discount.
By using Unbox, NBC is allowing users to purchase entire seasons of its shows at a discounted price. The current price for individual episodes is $1.99, the same as the iTunes store.
If customers follow NBC over to the new service, the move could provide a large boost to Unbox. Apple estimated that NBC shows accounted for 30 per cent of all TV show purchases on iTunes.
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