... "If Linux runs on every architecture, why should another operating system be in its way? " ...

Cooperative Linux is the first working free and open source method for optimally running Linux on Microsoft Windows natively. More generally, Cooperative Linux (short-named coLinux) is a port of the Linux kernel that allows it to run cooperatively alongside another operating system on a single machine. For instance, it allows one to freely run Linux on Windows 2000/XP, without using a commercial PC virtualization software such as VMware, in a way which is much more optimal than using any general purpose PC virtualization software. In its current condition, it allows us to run the KNOPPIX Japanese Edition on Windows (see Screenshots).

http://www.colinux.org/