"The idea of this project is to allow a Linux Kernel to run at
the same time (cooperation) with the Windows system instead of
doing virtualization or emulation. The result is an amazing speed
if compared to VirtualBox or other virtualization solutions
expecially in I/O and network operations.
coLinux can run as stand-alone application (you get a console
with working virtual TTYs) or as a system services. It can be
insalled on Windows 2000, XP, Vista and Windows 7. Only 32bit mode
is supported at this time but 64bit support is under work thanks to
a $5,000.00 sponsorship they got.