Apple TV owners have been warned they must wait a few more weeks before the promised software update for the set-top box appears.

In a press release confirming that MacBook Air units have begun to ship in the US, Apple warned: "The new Apple TV software update, which allows users to rent high definition movies directly from their widescreen TVs, is not quite finished. Apple now plans to make the free software download available to existing Apple TV customers in another week or two."

While film rentals aren't to be made available outside the US initially, the much-anticipated update offers additional features for customers in other countries.

The update will empower the Apple TV to browse and download podcasts and buy music directly from iTunes, with purchases made automatically synced to a user's primary computer.

Apple TV users will also be able to view photos from their computers, Flickr and .Mac Web Galleries on their widescreen TV as slideshows or screen savers.