Amazon yesterday unveiled the Unbox Video Store, a direct rival to Apple's iTunes 24-7 video store, which allows users to buy or rent TV shows, movies and other video content from the internet.

Amazon Unbox is offering thousands of DVD-quality videos from more than 30 movie and TV studios, which can be stored on up to two PCs and two portable video players at once, the company said. When a user downloads a movie or show, Unbox automatically sends a second download file optimised for Windows Media-compatible portable devices. It also keeps track of media purchases on a personal page at Amazon's Your Media Library, and acts as a backup, allowing users to download video purchases onto an additional PC.

Unbox is one of many new services aimed at capturing the growing interest in downloading video from the internet. The service will compete with similar video download stores such as Apple's iTunes, and is a direct threat to traditional DVD services from companies such as Blockbuster and Netflix.

Amazon Unbox is offering a $1.99 (about £1.05) rebate on a user's first purchase, enough for one free TV show. But new users will have to enter their credit card information into the system first as part of the registration process, and then download the Amazon Unbox Video Player software.

Unbox is charging between $7.99 (£4.25) and $14.99 (£8) for most films, and rentals of the latest movies for $3.99 (£2.15).

Videos can also be sent as a gift. The company's Unbox RemoteLoad technology enables users to buy video from one PC, such as their home computer, and download it to another, Amazon said.

Apple OS users can not shop at Unbox. The service only works on Microsoft's Windows XP. Users with older PCs may also find it difficult to meet Unbox's hardware requirements. At minimum, a PC needs a 1.5GHz processor and 512MB of memory, such as DRAM (dynamic RAM), in addition to a DirectX compliant video (64MB) and sound card. Users must also have an internet connection capable of sustained 800kbps data transfer rates, Amazon said.

Unbox is offering a host of special offers to attract new users. From 14 September until 27 September, for example, all of the final, cliffhanger episodes from the most recent series of CSI will be on sale for just $0.01 to promote the launch of the new series.

The company is also offering all 79 episodes of the original Star Trek series, including the pilot. Some of the movies available on Unbox include Inside Man, Failure to Launch, Walk the Line and V for Vendetta, as well as classics such as Ben Hur and The Poseidon Adventure. Some of the major movie studios signed on with Unbox include Universal Pictures, Sony Pictures and Warner Bros.