I've installed Oracle Virtual Box on a W7 machine. I then tried to download Mint, but instead of the ISO file appearing in 'Downloads' as expected it opened a new folder called New Folder (!). When I tried to add it to the Virtual machine I was only offered D (the DVD drive) and not the new folder. So I cannot load in Mint to try it.

OK, there is no virtualbox problem here because all of the things you are doing now need to be completed BEFORE you fire up VirtualBox. Virtualbox does not download software.

What are you using to download the ISO file? THERE is where your problem lives.
It is most common to use a browser (Mozill, Chrome, or Opera perhaps) and download using http. Where the file lands will depend upon your download settings in the browser.

Are you following any tutorial, how-to, WIKI, or other documentation?
If we have access to the steps you are following, and know what step you have a problem with, we might be able to provide more targeted assistance.

Thanks. I am following http://everydaylinuxuser.com/2014/05...s-virtual.html.

Point 1 and 3 are OK, but point 2 (at the end) does not come to the downloads page. That is where the only think offered is my optical drive D

Thanks. I am trying to follow http://www.everydaylinuxuser.com/201...s-virtual.html

Point 1 and 3 are OK. Point 2 hangs up at the end. I am not offered the downloads directory. This is where I get Optical drive D.

At step 2 you are simply downloading the iso. Of the links provided, which have you chosen? (from this page)

Do you mean at the stage "Click on the folder icon and navigate to your downloads folder and select the Linux Mint ISO file downloaded in step 2." you cannot see the downloaded .iso file? If so, you are clicking on the folder icon on the right and not trying to find it in the drop-down box, I take it?

Cinnamon 32 bit (save rather than run)

Yes, that's it. Cannot now remember for sure. I think I tried both drop down box and the other.

Clicking on the folder should give you a file explorer, from which you will have to navigate to wherever you downloaded Mint to in step 2. I take it in Step 2 it took ages to download then you were invited by the browser to to pen the containing folder, or similar? That should let you know where it is.

I've just tried again. I get a small dark screen with Linux Mint at the top of it, but nothing else (it says at the top 'Linux Mint running'). If I click on it I get messages about capture

I take it you managed to add the .iso file? If so, that means it's (sort of) working -- did it show a screen with Oracle VirtualBox or similar before it went black? You might need to wait a short while for Mint to boot up depending on how fast your hardware is.
If you didn't get the option to add the .iso file you might need to do it manually by changing the settings for the virtual machine and making the virtual optical drive point to it.

Well I'm not sure if I did manage to add it. The system said 'booting' and counted down, but then nothing happened.

mp100,

I recommend burning the Linux Mint .iso file to a DVD and inserting this in your optical drive.

Next, under “Section 5-Install Linux Mint”, select your optical drive (probably D: or dev/sr0). This should be selected automatically.

Then click on Start.

You need to wait a minute or two before things proceed.

I have successfully installed into VirtualBox both 32 and 64 bit versions of Linux Mint 17.2 MATE, amongst several other Linux OSs.

It might be easier to get rid of that VM and start again, this time being very vigilant what happens when you're asked to select the boot medium. As I mentioned you should get a file open dialogue from which you browse to the .iso file you downloaded. Without knowing which part of this is giving you problems there's not much can be done to help.
beachboy2 is right in that it might be easier to burn to DVD then install but that means having a blank DVD, knowing how to burn (which isn't necessarily as easy as it sounds) and spending more time installing as it's generally slower to install from a real optical drive than a .iso file, at least in my experience.

Yes, understood. I am quite happy about preparing a blank DVD, but my instinct is to follow the thread (I gave the URL)and do what is suggested there. In particular I am puzzled as to why the downloads do not go to a download folder, but always to 'New folder' (and changing its name afterwards doesn't make any difference ether)! I've tried both saving and running the downloaded file