I love beta software. It gives you the chance as a consumer to evaluate the software before you buy it. To try out a new operating system without exposing my hard drive and accessories directly to the OS, I use Sun's free, open-source Virtualbox. Virtualbox holds and contains the operating system within the operating system you are currently running. This virtualization allows you to totally control the operating system without having to have an extra computer on hand.
In order to install Windows 7, you must go to Microsoft and download the ISO for Windows 7 and obtain a key. Link
Virtualbox can be downloaded Here.