virtualbox.org

When cloning a vm do you need extra license keys for the os for instance or are these just cloned?

Are you asking a technical or a legal question? Technically, if you clone a working installation you get another working installation. You are not rerunning Windows setup and will not be asked for another CD key. If you change the virtual hardware in a significant way then you may be asked to reactivate.

If you're asking if you're legally entitled to create clones of a working Windows installation - well you should really ask Microsoft about that if you want a definitive reply. My own feeling is that if the clones are not run at the same time then it should be ok. Clones effectively allow you to have a variety of specially tailored installations ready to use, all variations on the same install. Cloning is made easier by VMs, but you could also do it at the physical level using imaging software (Ghost, Acronis etc) - so being virtual is not IMHO at the core of the question.

And of course: ultimately, if the Windows license is too restrictive for your needs then perhaps you should consider abandoning Windows, and switching to eg. Linux. With Wine you may even still be able to run some of your old apps.