Office Web Apps Beta went live today and people have already started to compare it with Google Docs and Zoho. Though I have personally not used it yet expect a full review from the staff pretty soon.
In the initial period not everyone will be able to make use of the new office web applications. You will have to wait for a invitation to test out Office web Apps beta.
Invites will be sent out to users who upload documents to SkyDrive first.
If you do not do that, to get in the wait line for a Office web apps beta invitation go to the registration page and register yourself for the Technical preview of office 2010 and office web apps beta.