To move the images to another library you will need to use the command Export as library. This will create a new library with the images and all their metadata. Then you can open the other library and import this library into it.
You can export as library any structure in the Aperture library so for example if all the images are in one project you can export that project as a new library. If the images are spread out over multiple projects you can create an album (either regular or smart) and export that as a new library. If it is only a few images you can simply select the images and export those.
Once you have the images in the new library you can copy this library to the other system and after opening the library you want to add thee images to, run Import library.
Note exporting the images from the original library will not delete them from the library. If you don;t want them in the original library anymore once you've moved them you will need to delete them yourself.