Here is a C&P from the freeware group I frequent, mentioning other possibilities:



> http://www.andlinux.org/index.php
>
> "andLinux is a complete Ubuntu Linux system running seamlessly in
> Windows 2000 based systems (2000, XP, 2003, Vista, 7; 32-bit versions
> only). This project was started for Dynamism for the GP2X community, but
> its userbase far exceeds its original design. andLinux is free and will
> remain so, but donations are greatly needed."
>
> "andLinux is not just for development and runs almost all Linux
> applications without modification."
>
> Requirements
> OS: Windows 2000 / XP / 2003 / Vista / 7 (currently only the 32-bit
> versions are supported)
> Memory: at least 128 MB (192 MB or more is recommended) Note that you
> should have enough memory left for Windows (at least 128 MB for Windows
> 2000 / XP / 2003; at least 512 MB for Windows Vista / 7)! Hard disk
> space: 2.5 GB (XFCE version) / 4.5 GB (KDE version) Note that you need
> an NTFS file system (which is default since Windows 2000) because you
> can't create files larger than 2 GB on FAT(32) file systems!
> A good internet connection (to be able to install further applications
> via apt-get / Synaptic)
> Some basic Linux skills to proceed once andLinux is installed
>
> Downloads
> http://www.andlinux.org/downloads.php
>

Latest beta is May,2009,getting a bit dated.Similar but a little more
current is coLinux http://www.colinux.org/
"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/Vista/7, 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"