if you want to import another object, such as a DVD player into your scene that you made in another maya scene or project, you would import it as a 'reference'
Import/reference; and then group it and give it a name.., eg; 'DVDreferance.'
not much piont in that unless the project is super huge, as in a movie rather than a scene, in this case as said.., use layers.
take it easy and life will be easy