From techcrunch:

"We had guessed earlier this year that Microsoft would choose the Silverlight platform to deliver Office online, but Microsoft will instead be copying the Google approach - the applications will be 100% HTML and Javascript."

This article says that it will be Silverlight. Tempted to trust TC on this one.

according to readwriteweb it will include js,html, and silverlight, as one would expect.

http://www.readwriteweb.com/archives/microsoft_office_comes_...