The price of a high-definition TiVo box is dropping substantially.

Today, the company is announcing the $300 TiVo HD with a 160 gigabyte hard drive that's to be available starting in August. Until now the only HD option from TiVo was the 250 gigabyte Series 3 model that lists for $800 but is widely available for about $600.

The TiVo HD has the same connections (including HDMI) as the Series 3, but it lacks the fancier display and the THX-certified output of the higher end model.

TiVo

The TiVo HD will work with Amazon.com's Unbox video dowloading service.

Microsoft's Xbox 360 also downloads and records high-definition video and starts at $300 as well. (Update: Record isn't the right term; it can store downloaded material but doesn't record off the air TV. It can also play recorded TV stored on a Media Center PC elsewhere in the house).

Microsoft also sells high-definition video downloads, which aren't yet available for the TiVo HD. TiVo also won't immediately activate the HD downloading capability, but it's in the works, said Jim Denney, vice president of product marketing.

There isn't much rush. The device works with Amazon.com's Unbox video downloading service, which doesn't yet offer HD downloads. Still, I'll bet TiVo will sell a ton of the new devices and in turn boost Unbox.

Also in the works, but not ready yet, is the option of expanding the TiVo HD's storage capacity with an external hard drive. The box has a fast eSata port but it won't work until TiVo provides a software upgrade. Creative Series 3 users have figured out a hack to add external drives, Denney noted, but the hack won't work on the TiVo HD.

Denney said TiVo plans to allow external drives but isn't ready yet:

"That is certainly our intention. We're working through some last minute issues with some of our vendors to make sure everything is lined up."

TiVo also competes with set-top boxes offered by cable companies and PCs running Microsoft's Media Center software, both of which can record HD content.

Media Centers were pretty competitive with the Series 3 on price -- you could go either way for about $800, and Microsoft doesn't charge a monthly service fee like TiVo.

Vista Media Centers should also get traction this fall as new and cheaper video cards and systems with HDMI connectors appear, unless people decide they can get by with a $300 TiVo HD.

Of course, both systems could be obsolete in a few years, when more TVs are likely to be sold with ethernet jacks and wireless systems for connecting straight to the Internet.