coLinux is a port of the Linux Kernel to Windows which executes as a single process. Using Xming server one can easily run X apps on windows. IBM Developer works has an article on the same topic:
Virtualization with coLinux .. read
One of the best applications of
coLinux is andLinux which allows you to run Ubuntu Linux seamlessly on Windows 2000/XP/Vista machines .. read.LifeHacker has an article on
andLinux .. read