As part of a plan to expand to new platforms, on-demand movie service Vudu (owned by Wal-Mart) is partnering with online video service Boxee to debut its streaming movies on the PC and Mac computers.

Boxee has its own set-top box (pictured right) to hook up to a TV, due to launch in November. But you can also download Boxee’s free media center software to a PC or Mac machine and then view the videos on your computer. Now you will be able to watch Vudu’s high-quality streamed movies as well. Many of those movies, which include a huge collection of recent Hollywood hits, indie films and other new releases, are available for $2 for two-night rentals.

If you watch the Vudu movies on a PC or Mac via Boxee, you can see them in standard definition. But if you watch on the upcoming Boxee Box (made by D-Link), you can see them in high-definition formats with surround sound. Boxee says the Vudu content will give it the largest selection of HD movies anywhere.

Wal-Mart bought Santa Clara, Calif.-based Vudu back in the spring as part of a move into the digital distribution of movies. Edward Lichty, general manager of Vudu, said his company’s goal is to help spread its streaming movie content to as many platforms as possible.

Lichty said Vudu doesn’t disclose its user numbers, but he said the service was popular. Over time, he said, more promotion would be done to help the service spread, but he declined to say if Wal-Mart will be launching an ad campaign around Vudu soon. Vudu is also available on connected Blu-ray players and a number of web-connected TV sets. Eight consumer electronics companies are partners with Vudu.

Rivals include Apple’s Apple TV, Amazon, and CinemaNow. Vudu has 55 employees.