I have a loaner laptop that has MS Windows with locked down permissions. It works okay for what I need to do, but I started wondering if there was a way to install a separate Windows OS on a separate hard drive to do what I want to do on it.

Virtual

I wish I could use VirtualBox or VMWare, but that is not an option (I even tried VBox portable).

External Drive

My next trial was see if it was possible to install Windows on an external drive, and then plug that drive in and boot from it whenever I wanted my own OS. After a few Google searches, I see that is not really a possibility.

Swap Primary Drive

Another option, would be to get a second internal hard drive, take the existing HD out, and install a new Windows OS on the secondary HD. This would mean swapping the internal hard drive each time I want to switch OSs - doable, but not very convenient.

Dual Boot

The laptop has an expansion slot where a second hard drive can be plugged in quickly. I thought about Dual booting, but I don't want to mess with the MBR on the primary hard drive. When I have to give the laptop back, I don't want a dual-boot screen to popup.

Summary

Is there a way to have 2 hard-drives on a machine, each with it's own OS, and maybe use BIOS settings to have only 1 hard drive active at a time? That way both hard drives could be physically connected, but only one would actually be active at a time.

I basically want a second OS that does not (can not) affect the existing OS in any way, and can be removed at any time without affecting the existing OS. The secondary OS does not need any of the files on the main hard drive - it's basically like having 2 separate computers using the same hard ware...

Is this possible, or would it be easier just to go out and buy a different laptop?

Thanks in advance!

EDIT

I just discovered that my BIOS allows me to pick (at startup) which hard drive I want to boot from. I poked around in the BIOS and there is not a place to disable certain devices, like the primary hard drive. My only concern about plugging in a second hard drive and installing Windows to the second hard drive is that it will mess with the primary hard drive, or add a bootloader screen to pick which windows install to use.

My thought would be to physically unplug the primary, plug in the secondary and install windows to the secondary. After the install is working properly, I can plug the primary back in and use the BIOS feature to determine which drive to boot to. Is there any way after I have 2 separate installs on 2 separate hard drives that one of the installs could mess with the MBR on the other drive?