Running a guest OS on your host OS could be great. The thing is, the software you are using to do this should be free of cost . In order to use another OS while you are using your host OS is possible with Virtual Box. This software makes use of concept of Virtualisation. Instead of providing a full fledged explanation on what Virtualisation is, I would provide you an intro.

Virtualisation means creating a virtual computer on your physical computer.  It means you can have two OS running side-by-side at the same time on a single machine. Without Virtualisation, you’d need to either dual boot or install your second OS on a second machine.

After installing guest OS on your host OS, you can run your new (or old) OS.  Just start it up and experience the joy having one operating system boot up inside another.

Installation guide is available here.

Download Virtual Box.