I have Linux installed on my harddrive, sometimes I run it as the host operating system and sometimes run it as a guest in Windows using VirtualBox. It's a nice ability, I think.
I don't think it's possible with Windows though. Is it because your average distribution includes drivers for everything known to man? Are devices/drivers configured statically in Windows so when somethings changed it breaks?
Yes, Windows ties itself to a particular hardware configuration. It's mostly an anti-piracy thing, though -- you could always install the necessary drivers for Windows to run in VirtualBox, but Windows will scream about needing to reactivate itself every time you switch between the two.
You can run Windows as a guest on Virtual Box in Linux but you will need to do a clean reinstallation of Windows on the new virtual machine you create.
