QML Designer

In Qt Creator 2.0.1, the QML Designer was still in many ways unfinished, and very buggy (it would often crash Qt Creator). the QML Designer isdisabled by default. You'll need to enable it manually by going into Help -> About Plugins..., checking QmlDesigner, and then restarting Qt Creator. However, it is disabledfor good reason.

You should really upgrade to at least Qt Creator 2.1.0, or to the just released 2.2 beta.

I'd suggest going for the beta, since its QML Design mode has seen a bit of a rewrite since the 2.1 version, and you would have a chance of providing feedback about any bugs before the final version is out.