Sorry I did not quite understand the issue.
The downloading of linux will result in an ISO image. You can attach that to the virtual box as shown in my videos.
Are you getting any error? If yes, then please take a screen shot and upload it here. Thanks.
Also please keep in mind that if you are downloading 64 bit linux, then you might see unexpected errors which I may not be able to troublshoot and fix for you. Also my linux packages will not work for you. You might have to download your own. I have not tested 64 bit installation. You can follow my videos to the core if you want to avoid problems.