I have a very similar problem, but instead of crashing, the entire application hangs and never recovers, it has to be killed with Force Quit. I've discovered today that this affects Clip Art as well, since it's accessed by the browser. There are some helpful suggestions in the Office for Mac forums, at
http://www.officeformac.com/ms/ProductForums/Office/6935 but they don't work for me. I think switching to another user is not a helpful suggestion - I have 200GB of files and transferring them would be awkward and time consuming - with no guarantee of success.
Microsoft Support said deleting preference files didn't work for some users either. They gave up on my support call.
This 2011 version of the product seems to have some massive flaws, and overall I'm disappointed that I upgraded. I should mention that the media browser in Apple's Pages application has no problems at all, so it's not something about my user account that affects everything.