Owl's_Warder raises an excellent point: there are a number of sources for DVI-HDMI adapters.

Quick background: DVI was originally developed for PC's, to allow video cards to interface with flat panel LCD monitors that were purely digital devices (making the analog VGA interface useless). Encryption called HDCP (High Definition Copy Protection) was added to DVI and it was carried over to the home theater world as a secure means of passing a high definition digital video signal between devices. HDMI came along later, and uses effectively the exact same video protocol (there are some differences relating to black level, but the two are basically interchangeable) plus digital audio using a smaller plug.

The central advantage of HDMI over DVI is the ability to use a single cable for audio and video. The catch here is that to really benefit from this, you need to either be using your display as your audio source (blah) or you need to be able to pass both audio and video through your receiver. HDMI ports on displays and source components were almost unheard of less than a year ago, but have become a lot more common. HDMI ports on receivers remain pretty scarce, and many cases (such as the Panasonic that started this thread) lack the ability to switch between multiple HDMI sources - you get a single in and a single out. Denon does have a receiver with HDMI and DVI switching (one DVI and three HDMI inputs plus one output for each), but that receiver is the 5805 and the MSRP is $6,000.