Well, currently the only way to get at the trailer is to be a member of 'hyperspace' on the Star Wars website - which I'm not However, looking around on the web you can find the trailer elsewhere - and it's in good quality.
Star Wars Episode III: Revenge of the Sith
All the available trailers are quicktime - but fear not if you can't get them - the trailer is released in general with 'The Incredibles' in cinemas, and also will be released online in varying formats next week to everyone!
Yoda, 'see that - that's me - with a lightsabre - again!'