Extract the content into: <pentaho data integration folder>/plugins/steps/. When extracted there should be a folder inside the 'steps' folder called 'QVXWriterDemo'.
Start Pentaho Data Integration. Create a new transformation (or use an existing one). There should be a new entry in the 'output' steps category called "QVXWriter Demo Plugin".
Define a location and file name (.qvx) in the "Output File Location" field. Give the file a tablename in the second field. make sure your columns got the correct datatype (Integer, Number, Date, String). When you are not sure. Use the "Select values" step in Pentaho to manually add or change the meta values of your columns.
Note: This demo plugin is limited to write a maximum of 100.000 rows into a QVX file.
Note 2: On my blog I also use images to show how it should look like.