Hulu recently launched an HD Gallery featuring a selection of High Definition video clips at 1280 x 720 resolution.
You'll need a fast connection and a fast machine to watch HD Hulu. Check out their system requirement here. In a nutshell: a connection of 2,400 Kbps or higher (not your average home user speed) and the latest Adobe Flash Player 9 to stream these High Definition bandwidth clogging clips. Needless to say, this leaves out those who will be using this service on a Wii , aPS3 or an Xbox not to mention an iPhone.
Flash Player 9 is free to download here. It's the secret weapon that Hulu claims will make them the YouTube killer. No more crappy YouTube flash videos, baby. It's HD, baby...HD.