I was reading up on KVM and I was wondering if you can set it to boot the virtual machine from a different HD, instead of re-installing windows onto my Ubuntu drive?

Is that possible or do I just not have a complete understanding of how VM's work?

A KVM just switches the video output and keyboard/mouse input to a different machine. It allows you to use one monitor/keyboard/mouse on multiple machines.

That has nothing at all to do with a VM, or virtual machine, which allows you to run a second operating system from within another OS.

Kernal-based Virtual Machine

Sorry, I didn't specify things.

Alright, that makes things a little clearer.

To answer your question, I suppose it would depend on the software. Most of the virtualization applications I have used required that the OS being run was stored in an image file, rather than an actual device. Unless somebody knows of a VM that doesn't require that, you would need to install Windows in the VM manually.

Of course, that might not be such a bad thing. Windows does not take kindly to the hardware changing, so if you tried to run an existing installation in the VM, it would likely fail because the hardware being emulated would not be the same hardware it was installed under.