By my understanding, to import a Visio ORM model into NORMA, you need to:
1) Export the Visio ORM model to XML using Orthogonal Toolbox (available from http://www.orthogonalsoftware.com/products.html)
2a) Rename the exported XML file to have a '.orm' extension. At this point, if you double click on the ORM file, it should open in NORMA and be ...