I've downloaded an .iso file but don't have a DVD writer at the moment - is there a recommended Virtual DVD drive that I can use to install from the .iso file?
7-Zip will open ISOs too (as well as being generally superb.)
Assuming Windows, you can try Daemon Tools.
In Linux you can mount an ISO similarly to the way you mount other volumes:
mount -o loop -t iso9660 file.iso /mnt/test
Alternatively, if the installer doesn't mandate a "physical" volume to install from you can also extract the contents of the ISO file (archivers such as WinRAR are usually able to do this, but there's also special software for this) and run the installer from there.
I usually use PowerISO.
There are a few alternatives in this question providing that your are running Windows.
I'm using MagicISO myself and it works fine, although you have to buy a license to open ISO files larger than 300MB. An alternative is MagicDisc, a freeware virtual drive from MagicISO that can be used to mount ISO files as virtual drives.
There is a free program called AlZip that will let you open/extract an ISO file like a regular compressed file (zip, rar, etc) It also supports these other formats, of course. Get it here
edit: it used to be free (ad-supported) for non-commercial users, but they seem to have changed the policy recently...
Also check out all the other free utility programs this Korean company has created. I can't remember if it was AlZip, but one of them adds a very useful "create new folder" context menu item.
I use Total Commander plugin ISO:
It won't open certain ISO files though.
There are a lots of software and tools can mount an ISO file. I've tested 2 or 3 tools and Virtual CloneDrive is my favorite for win XP and 7. And win 10 comes with built in ISO mount/Unmount support. I also have a tutorial about this http://pointblankpro.com/how-to-mount-an-iso-image-in-windows/
And If you are on Linux Machine, Then you can use a single line command to Mount any ISO file to your linux machine. AskUbuntu has a thread about Mounting ISO's in Ubuntu https://askubuntu.com/questions/411793/mount-iso-using-the-terminal