Q: Is it possible to install OS X as a virtual machine ( eg. Using VMware) under  Windows OS (eg. Windows 7 ) ?

Apple do not licence OS X for virtualization on non-Apple hardware.

tt2

This is a user to user support forum. I'm afraid my knowledge is limited, but my understanding is that you are only permitted to run OS X on Apple hardware. If you start from a working Mac then you can install additional operating systems with boot camp or virtualization software. See http://www.macworld.co.uk/feature/mac-software/best-virtualisation-app-run-windo ws-on-your-mac-boot-camp-vmware-parallel…  for example.

Take a look at https://robb.weblaws.org/2015/10/17/os-x-el-capitan-license-in-plain-english/ In particular 4, 5, 10 and 11. If you want to run any hands-on OS X training then use Macs configured as Macs.

tt2

The license agreement for El Capitan says that you can only run it in a virtual machine on a Mac, and that said Mac has to be already running El Capitan. The host Mac cannot be running other OS X versions or different OSes.