To make mounted image appear as if it is a disc in a physical device, you can attach the virtual device to the physical one. In this case, you need to perform several steps:
Choose the device you want to attach. Note that it should be only SCSI or IDE drive.
Choose Attach to physical device... option from its contextual menu and then select the physical drive from the list.
Wait a few seconds. The drvie will be marked as attached, and an image mounted to it will appear in the physical drive too.
Also, you can attach a drive from the Device Parameters.... In this case, you will be able to adjust additional Media priority option that defines which one — a physical disc or an image — will be linked to the physical drive if both are inserted.
To detach a drive, go to its contextual menu and click on the physical drive again or choose Detach option. Note that only one drive may be attached to the physical device at a time.