Wubi is an Ubuntu installer for Windows that lets you install and uninstall Ubuntu from a Windows desktop. Wubi adds an entry to the Windows boot menu which allows you to run Linux. Ubuntu is installed within a file in the Windows file system (a loopmounted partition), this file is seen by Ubuntu as a real hard disk. That way the hard drive does not have to be repartitioned before the Ubuntu installation. The resulting Ubuntu installation is a “real” Linux system, not just a virtual machine. Wubi makes it easy for Linux newbies to play around with Ubuntu.
Wubi is Safe
It does not require you to modify the partitions of your PC, or to use a different bootloader.
Wubi is Simple
Just run the installer, no need to burn a CD.
Wubi is Discrete
Wubi keeps most of the files in one folder, and If you do not like, you can simply uninstall it.
Wubi is Free
Wubi (like Ubuntu) is free as in beer and as in freedom. You will get this part later on, the important thing now is that it cost absolutely nothing, it is our gift to you…
screen shots (installing Wubi from windows) :
For more information: Link
Wubi still a prototype so there’s some bugs at there. You can report a bugs at those link.