Though I'm sure many marketing folks will be quick to call it HD (it's incredible how lax the definition of "High Definition" is for online streaming), the highest quality streams available from NBCOlympics.com are 480p widescreen (848x480). A large portion of the content, particularly highlights and specials, will be available in 480p quality. This content will be delivered using an adaptive streaming technology developed by Microsoft for NBC Olympics. Adaptive streaming ensures reliable delivery of video streams to end users without buffering, stutter or glitches - by adapting the video data rate and quality to each user's bandwidth. To experience the full 480p quality video, make sure you use the Enhanced player interface (click that "Enhanced" button in the lower-right bottom of the player when it pops up) and have at least a 1.5 Mbps Internet connection.
The rest of the content (i.e. live broadcasts and their rewinds) will be streamed using traditonal single-bitrate methods and resolutions.