The cutesy-named Wubi is an Ubuntu Linux installer that runs inside Windows just like any application.
It sounds like what a three-year-old would call their ratty, old teddy bear, but Wubi is actually an application that allows Ubuntu to be installed from within Windows -- an alternative to running a virtual machine or running from a Live CD version.
The application they developed, known as Wubi, is an Unbuntu Linux installer that runs inside Windows and looks to Windows like just another application. Most of the files Wubi uses to load and run Ubuntu Linux reside in a single folder; the installer does not modify a system's disk partitions, bootloader, or any other vitals; and the whole affair uninstalls just as quickly and painlessly. (bmighty.com)
I hadn't heard of this before, but if you're trying to get Windows users to give Linux a chance, it might be a good training-wheel option. Has anyone else heard of this or tried it out?
In a related story, Michael Horowitz is explaining to Windows users, "Why you want (and need) a Linux Live CD." Horowitz is suggesting Live CDs as useful tools for troubleshooting and recovering files from Windows when it won't boot or gets infected with malware. Linux to the rescue!