If you are using some live connection to fetch data from BOE repository, then you will be prompted for credentials.
In recent versions of dashboards, you can select offline support in Document properties.
With this checked, once you refresh data in dashboard, you can save an offline copy by right clicking on it.
This offline copy will disable all connections, so you can not dynamically fetch data from database. But you can show demo using existing data in that snapshot.
To avoid resizing of swf files, you can use canvas container of fixed size and enable scroll bar. Or design the dashboard keeping the target monitor resolution in mind.