One thing I noticed is that if you would like to combine both flowcharts and UML diagrams in one file, it’s tricky.
Anyway, to be able to see and use the Vision UML functionality, make sure that when you start a new file you choose the Software/UML Model Diagram stencil. (At least this is how it is named in Visio 2003). Please note that the features I am describing will not be available if select another stencil when starting a new file.
Then you drag and drop the shapes on the page as usual. However when you double-click a UML shape or right-click and select Properties, you’ll see something like the properties in Describe.
There is a UML menu item on the top you may look at.
You may publish the whole file online as HTML and there is a handy zoom feature. Also the pages are named after the tabs in the file.
I hope its not too late and this helps.