"Portable Ubuntu" is a portable version of Ubuntu which runs side-by-side with Windows, without using virtual machines.
(To download, use this link instead: http://sourceforge.net/projects/portableubuntu/files/portableubuntu/Vers... )
It is a modified version of Ubuntu 10.4.3 LTS using Gnome.
For me testing on my USB3.0 Harddisk it is quite good and stable.
It is also possible to resize the image file using "tfile" (which also took me quite long to hunt for a download) and then expanding the partition by resize2fs inside Portable Ubuntu.
A portable launcher can be useful to dynamically mount the portable drive automatically.
In the config file, look for the line "shared_folder0=c:\" and this is the way it mounts the drive.
The appinfo.ini I am using:
Name=Portable Ubuntu Remix
Description=This project consist in a portable image of Ubuntu that could run in Windows as a native win32 application. You could execute Linux applications and integrate it in your Windows desktop.
DisplayVersion=Version 4 slimLZM2 (Ubuntu 10.4.3 LTS)
It is already possible for me to use it quite normal, but a launcher can mount the portable drive automatically, and even automatically setting the RAM options on different computers.
The reason I request this is because "Portable Ubuntu" is very useful when one has to work with Windows and Linux at the same time (perhaps because of a software only available on either platform)
This kind of portable software is also missing on PortableApps.com.